Image Authentication Techniques
Content
IMAGE AUTHENTICATION TECHNIQUES
A SEMINAR REPORT
Submitted by
MADHURENDRA KUMAR
in partial fulfillment of the award of the degree of
BACHELOR OF TECHNOLOGY
in COMPUTER SCIENCE AND ENGINEERING
SCHOOL OF ENGINEERING
COCHIN UNIVERSITY OF SCIENCE & TECHNOLOGY, KOCHI-682022
AUGUST 2008
DIVISION OF COMPUTER SCIENCE & ENGINEERING SCHOOL OF ENGINEERING COCHIN UNIVERSITY OF SCIENCE & TECHNOLOGY KOCHI-682022
Cerified that this is a bonafide record of seminar entitled
“IMAGE AUTHENTICATION TECHNIQUE”
done by the following student
MADHURENDRA KUMAR
of the viith semester,Computer Science and Eengineering in the year 2008 in partial fulfillment of the requirements to the award of Degree of Bachelor of Technology in Computer Science and Engineering of Cochin University of Science and Technology.
DHANYA K SUDHEESH SEMINAR GUIDE
Dr. David Peter S Head of the Department
Date:
ACKNOWLEDGEMENT
I thank my seminar guide Mrs. Dhanya k sudheesh, Lecturer, CUSAT, for her proper guidance, and valuable suggestions. I am indebted to Mr. David Peter S, the HOD, Computer Science division & other faculty members for giving me an
opportunity to learn and present the seminar. If not for the above mentioned peopl my seminar would never have been completed successfully. I once again extend my sincere thanks to all of them.
MADHURENDRA KUMAR
ABSTRACT Automatic video surveillance (AVS) systems are used for continuous and effective monitoring of dangerous and remote sites. Video data acquired by the automatic video surveillance system can be recorded and presented as a proof in front of court law. But digital video data lacks legal validity due to the ease to manipulate them without leaving any trace of modification. Image authentication is the process of giving a legal validity to the video data. By authentication technique content
tampering can be detected and we can indicate the true origin of the data. There a two types of authentication schemes, which are
1. Cryptographic data authentication.
2. Watermarking-based authentication.
In this presentation an attempt is made to present the basic features of the image authentication techniques.
TABLE OF CONTENTS
CHAPTER NO. 1 2 3 4 5. 6. 7. 8. TITLE ABSTRACT LIST OF FIGURES LIST OF SYMBOLS INTRODUCTION AUTOMATIC VISUAL SURVEILLANCE SYSTEM AUTHENTICATION TECHNIQUES CRYPTOGRAPHY CRYPTOGRAPHIC DATA AUTHENTICATION 8.1 DRAWBACKS OF CRYPTOGRAPHIC AUTHENTICATION 9. WATERMARKING 9.1 CLASSIFICATION OF WATERMARKING AUTHENTICATION SCHEMS 9.2 REQIREMENTS OF W ATERM ARKING BASED VS DATA AUTHENTICATION 10. WATERMARKING ALGORITHM 15 13 10 11 PAGE NO iii v vi 1 2 3 4 8
10.1 WATERMARK GENERATIONAND EMBEDDING 15 10.2 WATERMARK DETECTION 10.3 AUTHENTICATION CHECK 17 18
11. 12. 13. 14. 15.
OTHER APPLICATIONS ADVANTATGES DISADVANTAGES CONCLUSION REFERENCES
19 20 21 22
23
LIST OF FIGURES
SI NO 2.1 4.1 5.1 6.1 7.2
IMAGES
PAGE NO 2 4 6 12 17
Automatic Visual Surveillance System Encryption and Decryption Cryptogarphic Method Types of Watermarking Watermark Detection
List of Symbols, Abbreviations and Nomenclature
SI. NO.
ITEM AVSS
VS
DEFINITION Automatic Visual Surveillance System Visual Surveillance
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Image Authentication Techniques
1. INTRODUCTION
This paper explores the various techniques used to authenticate the visual data rec used for continuous and effective monitoring and reliable control of remote and advantage of the potentiality of VS system. The validity of visual data acquired,
by the automatic video surveillance system. Automatic video surveillance systems are
dangerous sites. Som e practical issues m ust be taken in to account, in order to take
processed and possibly stored by the VS system , as a proof in front of a court of law w ithout leaving any visible trace of the m odification. S or im age data have no o digital
one of such issues. But visual data can be m odified using sophisticated processing t
value as legal proof, since doubt would always exist that they had been intentionally created artificially by computerized techniques su as morphing. Therefore the true ch origin of the data m ust be indicated to use them as legal proof. By data authenticat indicating their true origin.
tam pered with to incrim inate or exculpate the defendant. Besides, the video data ca
m ean here a procedure capable of ensuring that data have not been tam pered w ith
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2. AUTOMATIC VISUAL SURVEILLANCE SYSTEM
Automatic Visual Surveillance system is a self monitoring system which consists of a video camera unit, central unit and transmission networks.(figure)
2.1 Automatic Visual Surveillance System
A pool of digital cameras is in charge of frame the scene of interest and sent
corresponding video sequence to central unit. The central unit is in charge of analyz
the sequence and generating an alarm w henever a suspicious situation is detected. provider, the police departm ent or a security guard unit. Som ewhere in the system
unit also transm its the video sequences to an intervention centre such as security service
video sequence or som e part of it m ay be stored and w hen needed the stored seque to be legally credible, som e m eans m ust be envisaged to detect content tam pering reliably trace back to the data origin
can be used as a proof in front of court . If the stored digital video sequences have of law
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Image Authentication Techniques
3. AUTHENTICATION TECHNIQUES
Authentication techniques are perform ed on visual data to indicate that the data is
forgery; they should dam age visual quality of the video data. At the sam e tim e, th not
techniques must indicate the malicious modifications include removal or insertion o
certain fram es, change of faces of individual, tim e and background etc. Only a prope for authenticating video data. They are as follows
authenticated video data has got the value as legal proof. There are two m ajor techni
3.1 Cryptographic Data Authentication
It is a s tra ig h t fo rw a rd w a y to p ro v id e v id e o a u thnean tic a tio nthrough the joint m e ly , use of asymmetric key encryption and the digital Hash function.
Cameras calculate a digital summary (digest) of the video by means of hash functio
Then they encrypt the digest with their private key, thus obtaining a signed digest which
is transm itted to the central unit together w ith acquired sequences. This digest is us public key of the camera.
prove data integrity or to trace back to their origin. Signed digest can only read by u
3.2 Watermarking- based authentication
W aterm arking data authentication is the m odern approach to authenticate visual da imperceptibly embedding a digital watermark signal on the data. Digital w aterm arking is the art and science of em bedding copyright inform ation in the original files. The inform ation em bedded is called ‘waterm arks Digital waterm arks are ‘. difficult to rem ove without noticeably degrading the content and are a covert m ean situation where copyright fails to provide robustness.
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4. CRYPTOGRAPHY
M ounting concern over the new threats to privacy and security has lead pread s to wide mainly two functions
adoption of cryptography. Cryptography is the science of transform ing docum ents. I
♦ Encryption ♦ Decryption
The purpose of encryption is to render a docum ent unreadable by all except those w
authorize to read it. Cryptographers refer to the content of the original docum ent as p The key is a randomly selected string of numbers.
text. Plain text is converted in to cipher form using an algorithm and a variable or ke
PLAIN TEXT
CIPHER TEXT
ENCRYPTION KEY
ENCRPTION ALGORITHEM
DECRYPTION KEY
DECRYPTION ALGORITHEM
CIPHER TEXT
PLAIN TEXT
4.1 Encryption and Decryption
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Only after decoding the cipher text using the key the contentdocum ent is revealed the of to the common people. Encryption schemes are classified in to :
1. Symmetric encryption In which the same key is used to both encode and decode the document. 2. Public key or asymmetric encryption
It requires a pair of keys: one for encrypting the plain text and the other for decrypting the same pair
the cipher text. A file encrypted w ith one key of a pair can be decrypted w ith other k
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5. CRYPTOGRAPHIC DATA AUTHENTICATION
To authenticate visual data each video cam era is assigned a different public or priva key private key of any particular camera can be decrypted with its own public key. This property is used to provide center authentication that is to trace back to origin of the true the data.
pair, with private key hardwired within the cameras. A document encrypted with the
5.1 Cryptogarphic Method
Before sending the video sequence to the central unit, cameras calculate a digital
sum m aryor digest of the video by m eans of a proper hash function. The digest is the
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encrypted with their private key. Encryption is done by considering the digitized val the brightness of each pixel. Digital signal is a sequence ofzeros and ones and it is
encrypted with the private key using a proper algorithm . The signed digest thus obt is then transmitted to the central unit together with the acquired visual sequence. Later the signal digest is used to prove data integr to trace back to their origin. The ity or
signed digest is read using the public key of the cam era which produce the video an same hash function.
check if it corresponds to the digest derived from the decrypted video content using
Any m anipulation the data w ill change the calculated im age digest derived from the of
decrypted data. Any discrepancy between the decrypted digest and calculated imag data is genuine. Value of the visual data can be added by tying each fram e to the particular label of of creation of each frame. Any modification of either the date time could be easily or revealed since it would change the locally calculated image digest.
digest indicate that the data has been tam pered, w ith identical digest indicates that
instant the fram e has been produced yet. This can be achieved by printing date and
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5.1 DRAWBACKS OF CRYPTOGRAPHIC AUTHENTICATION
Even though cryptographic data authentication is highly resistant to content tam per suffers from few drawbacks. They are as follows: 1.Knowledge of private key If the manipulatorknows the private key of the camera, he can change the digest to a thing is very small because the private key is hardwired within the camera. 2.Impossible to distinguish between malicious and innocuous modification It is difficult to distinguish between malicious and innocuous manipulations if cryptography is used. Innocuous modifications include compression of the video
involve the m odifications he had m ade on the actual sequence. But the possibility o
sequences. These m odifications are usual ly perform ed by the central unit w hereas diges correspondence between the digest and data would be lost. 3. High requirements of video camera
is calculated on the basis of the uncom pressed data by the cam era. So on com press
To avoid the above discussed problem , the video cam era should perform the com pres high computation as storage requirements. 4. Delay in transmission Digest calculations and encryption introduces a delay in transmission of video
of the video sequences prior to digest calculation. This requires the video cam era to
documents. This is harmful in system where the timely generation of alarm is critica
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5. Protecting privacy is difficult calculated digest.
A part of the program cannot be rem oved for privacy reasons since it will alte
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6. WATERMARKING
A digital waterm ark is a signal that is im perceptibly em beddeddigital data. This within about the host data. Digital w aterm ark is a signal which added to a docum ent to authenticate it and to p the ow nership. A com m only encountered w aterm ark is the logo m ost television digital
signal can be detected or extracted by m eans of com putations to m ake som e assert
channels display on the top of the television screen. Not only does it advertise the c recording. Watermark task consists of two main steps
but also provides the legal benefit of having a source signature persist during video
1. W aterm ark casting:-in w hich the signal represented by the w aterm ark is transm it o v e r th e c h a n n e l, th a t is in w a te rm a rk c a s tin g a n e n c o d etakesca host image r fu n tio n ‘f’ and a watermark ‘w’ and generate a new image Fw= (f, w)
2. Watermark detection:-in which the signal is received and extracted from possibly corrupted image.
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6.1 CLASSIFICATION OF WATERMARKING AUTHENTICATION SCHEMS
The characteristics of waterm arking system largely depend on its application scenar
For instant copy w rite protection application require that the w aterm ark is robust ag transform ation of host docum ent. Tw o approaches for w aterm arking data authe ntication are possible: 1. Fragile watermarking 2. Robust watermarking
m ost com m on data m anipulation,ie its presents can still be detected after nondestru
Fragile waterm arking refers to the case w here w aterm ark inserted w ithin the data is is taken as evidence that data has been tam pered w ith, whereas the inform ation co within data used to demonstrate data origin
or altered as soon as host data undergoes any m odification. W aterm ark loss or alter
In case of robust w aterm arking a sum m ary of the candidate fram e or video sequenc also with the summary. To prove data integrity the information conveyed by the mismatch is taken as an evidence of data tampering. The capability to localize the manipulation will depend on the summary of which is embedded in to the image.
com puted and is inserted w ithin video sequence. Inform ation about the data origin i the
w aterm ark is recovered and com pared w ith the actual content of the sequence. The
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WATERMARKING
FRAGILE WATREMARKING
ROBUST WATERMARKIN G
INVISIBLE WATERMARKIN G
VISIBLE WATERMARKING
DUAL WATERMARKIN G
6.1 Types of Watermarking 6.1.1 ROBUST VERSUS FRAGILE WATERMARK
Sem i fragile w aterm ark is m ore m ature than robust waterm arking. Tam per localizat easier in fragile watermarking but it is difficult to distinguish between malicious and innocuous manipulations.
Im age authentication by m eans of robust waterm arking is very prom ising w ith regar technique depends on the number of bits that can be hidden in to the image.
the distinction betw een m alicious and innocuous m anipulations. The robustness of s
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6.2 REQIREMENTS OF WATERMARKING BASED VS DATA AUTHENTICATION
In order to highlight the peculiarities of VS data authentication. Let us consider the m common requirements for watermarking authentication techniques. 1. The authentication technique not deteriorate the visual quality of data quality. m ust acquired to visual data. 3. The authentication technique should not consider innocuous m anipulation, e.g., im age compression and zooming, as valid authentication attacks. 4. It should be difficult for unauthorized person to forge an authenticated image. persons. 6. The authentication checking procedure should localize data tampering.
2. The authentication technique should be able to identify any unauthorized process
5. The authentication checking procedure should be easily performed by authorized
By considering particular cases the requirem ent for the authentication of VS data ar following.
6.2.1 THE INVISIBILITY CONSTRAINT
The requirem ent on the deterioration ofvisual quality of authenticated data is usuall the referred to us as invisibility constraint. The authentication technique m ust not deteriorate the visual quality of data. In this case how ever this is not crucial issue since VS do not exhibit a com parable that of quality
visual data used in a m edia. VS data acquired by inexpensive, low quality devices. V
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analysis w ould possibly be carried out in a low court will focus on the sem antic conten of the image, rather than on their visual quality.
6.2.2 MALICIOUS VERSUS INNOCUOS MANIPULATIONS
The authentication technique should be able to identify any nonauthorized or m alicious consider innocuous manipulation Eg: Image compression or Zooming, as valid authentication techniques. W hen data com pression is done in central unit the authentication is perform ed before com pression and m ust survive it. To satisfy privacy com plaints, som e processing is which are unimportant on the law point of view. This kind of processing as to be considered as m alicious w hen inform ation that is im portant for a court law is rem ov A solution to this problem is offered by authe ntication techniques capable of localizing to decide if it is malicious of innocuous.
processing occurred to the visual data. Besides the authentication technique should
on the authenticated video, before it is stored. E.g. for obscuring the faces of person
considered as innocuous. On the other side, the same processing procedure as to be
m anipulations. Once the m odification is precisely localized, it w ill be up to the court
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Image Authentication Techniques
7. WATERMARKING ALGORITHM
A watermarking algorithm for VS data authentication based on semi-fragile watermarking of each frame of the video sequenceis described in this section. The various steps for the watermarking process are as follows.
7.1 WATERMARK GENERATION AND EMBEDDING
Watermark generation aims at producing a binary or ternary watermark W(X) using cam era that has captured the im age. The block diagram of w aterm ark generation a embedding is shown below.
digital key K and host im age f(x). waterm ark key corresponds to the im age owner o The
In the proposed m ethod as indicating in the figure the waterm ark generation by usin pseudo random number generator and appropriate thresholding.
The w aterm ark key used for waterm arking a specific fram e in the sequence is com p provides the advantage of producing frame–dependent watermarks. To perform authenticity check, the detection should first know the fram e num ber in sequence which is always zero. Watermark embedding is performed by altering all the pixels of the original frame according to the following formula. Fw(x) = f(x) if w(x) = 0
of the cam era id and fram e num ber. Generating the w aterm ark key using fram e num
In this case, fram e rem oval or fram e substitution can be easily detected as non auth
g 1 (f(x ) , n (x ))if w(x) =-1
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Image Authentication Techniques
g2 (f(x), n(x) if w(x) =1 Where g1g2 are suitably designed function based on x. n(x) denotes a function that depends on neighborhood of x.
The function g1g2 are called em bedding function and are selected so as to detect th watermarked image fw(x), produces the watermark w(x). D (fw(x), N(x)) = w(x)
inverse detection function. D (fw(x), n(x)). The detection function, w hen applied to t
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7.2 WATERMARK DETECTION
In the w aterm ark detection procedure, the detector generates first the water m ark f the frame number are needed.
fram e to be checked. To do so, the id num ber of cam era that produce the sequence
7.2 Watermark Detection
watermarked image a detection image d(x) is produced. d(x) = D (fw(x), n(x)) Now we frame the false detection image given by
A detection function D is defined such that by applying the detection function to the
E w (x ) = 1if w(x) 0 and w(x) d(x) 0 otherwise
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The false detection image has value 1 if a watermarked pixel is falsely detected and otherw ise. The w aterm arked detection ratio is given by the ratiocorrectly detected of the pixel to the sum of the watermarked pixels in the image.
7.3 AUTHENTICATION CHECK
Authentication check is a tw o level process. A first level decision on im age authentic is taken by com paring the w aterm ark detection of the text im age w ith a pre specified threshold T.
If the first level decision test indicates that the im age is som ehow altered but authe second level decision test should be performThis test indicates whether the ed.
alternations m ade on the im age are concentrated in certain regions (Malicious tam p or one spread on the image (innocuous alternations).
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8. OTHER APPLICATIONS
1. To protect the intellectual property right of a music publisher who distributes music scores over digital media.
Digital piracy is a serious concern to the musical industry.Customers receive easily. By using image score watermarking we can prevent this. 1. It canbe used for everything from sending e-m ail and storing m edical record and legal contracts to conducting on-line transactions.
m usic in digital data form at and such data can be pirated and redistributed ve
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9. ADVANTATGES
1. Robustness to high quality lossy image compression. 2. Automatic discrimination between malicious and innocuous manipulations. 3. Controllable visualdeterioration of the VS sequence by varying the watermark embedding power. 4. Watermark embedding and detection can be performed in real time for digital data.
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10. DISADVANTAGES
1. Frame independent watermark can be easily found by comparative analysis of all image sequence frames and then could be easily added again to fake frames. 2. The detector should know the fram e num ber in order to perform authenticity che
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.
11. CONCLUSION
In these modern eras, visual surveillance system finds application in almost all fields ranging from com m ercial to defense. The video data acquired system are form ing by VS vital evidence for several legal situations. So for such situations, the importance of authenticating their content is very high. Cryptography and watermarking based authenticating techniques are quite safe and efficient for this and they are likely purpose to remain for quite for some while.
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12. REFERENCES
1. C. Ragazoni, G.Fabri, “Image Authentication Techniques for VS”, Proceedings IEEE, October 2001.
2. “Digital Watermarking for protecting piracy Electronics for you, January 2003. ”, 3. “Encryption wars”, IEEE Spectrum, April 2000. 4. M.M.Yeung and F.Mintzer “A watermark for digital image” IEEE Spectrum, April 2002. 5. www.ctr.columbia.edu
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A SEMINAR REPORT
Submitted by
MADHURENDRA KUMAR
in partial fulfillment of the award of the degree of
BACHELOR OF TECHNOLOGY
in COMPUTER SCIENCE AND ENGINEERING
SCHOOL OF ENGINEERING
COCHIN UNIVERSITY OF SCIENCE & TECHNOLOGY, KOCHI-682022
AUGUST 2008
DIVISION OF COMPUTER SCIENCE & ENGINEERING SCHOOL OF ENGINEERING COCHIN UNIVERSITY OF SCIENCE & TECHNOLOGY KOCHI-682022
Cerified that this is a bonafide record of seminar entitled
“IMAGE AUTHENTICATION TECHNIQUE”
done by the following student
MADHURENDRA KUMAR
of the viith semester,Computer Science and Eengineering in the year 2008 in partial fulfillment of the requirements to the award of Degree of Bachelor of Technology in Computer Science and Engineering of Cochin University of Science and Technology.
DHANYA K SUDHEESH SEMINAR GUIDE
Dr. David Peter S Head of the Department
Date:
ACKNOWLEDGEMENT
I thank my seminar guide Mrs. Dhanya k sudheesh, Lecturer, CUSAT, for her proper guidance, and valuable suggestions. I am indebted to Mr. David Peter S, the HOD, Computer Science division & other faculty members for giving me an
opportunity to learn and present the seminar. If not for the above mentioned peopl my seminar would never have been completed successfully. I once again extend my sincere thanks to all of them.
MADHURENDRA KUMAR
ABSTRACT Automatic video surveillance (AVS) systems are used for continuous and effective monitoring of dangerous and remote sites. Video data acquired by the automatic video surveillance system can be recorded and presented as a proof in front of court law. But digital video data lacks legal validity due to the ease to manipulate them without leaving any trace of modification. Image authentication is the process of giving a legal validity to the video data. By authentication technique content
tampering can be detected and we can indicate the true origin of the data. There a two types of authentication schemes, which are
1. Cryptographic data authentication.
2. Watermarking-based authentication.
In this presentation an attempt is made to present the basic features of the image authentication techniques.
TABLE OF CONTENTS
CHAPTER NO. 1 2 3 4 5. 6. 7. 8. TITLE ABSTRACT LIST OF FIGURES LIST OF SYMBOLS INTRODUCTION AUTOMATIC VISUAL SURVEILLANCE SYSTEM AUTHENTICATION TECHNIQUES CRYPTOGRAPHY CRYPTOGRAPHIC DATA AUTHENTICATION 8.1 DRAWBACKS OF CRYPTOGRAPHIC AUTHENTICATION 9. WATERMARKING 9.1 CLASSIFICATION OF WATERMARKING AUTHENTICATION SCHEMS 9.2 REQIREMENTS OF W ATERM ARKING BASED VS DATA AUTHENTICATION 10. WATERMARKING ALGORITHM 15 13 10 11 PAGE NO iii v vi 1 2 3 4 8
10.1 WATERMARK GENERATIONAND EMBEDDING 15 10.2 WATERMARK DETECTION 10.3 AUTHENTICATION CHECK 17 18
11. 12. 13. 14. 15.
OTHER APPLICATIONS ADVANTATGES DISADVANTAGES CONCLUSION REFERENCES
19 20 21 22
23
LIST OF FIGURES
SI NO 2.1 4.1 5.1 6.1 7.2
IMAGES
PAGE NO 2 4 6 12 17
Automatic Visual Surveillance System Encryption and Decryption Cryptogarphic Method Types of Watermarking Watermark Detection
List of Symbols, Abbreviations and Nomenclature
SI. NO.
ITEM AVSS
VS
DEFINITION Automatic Visual Surveillance System Visual Surveillance
1 2
Image Authentication Techniques
1. INTRODUCTION
This paper explores the various techniques used to authenticate the visual data rec used for continuous and effective monitoring and reliable control of remote and advantage of the potentiality of VS system. The validity of visual data acquired,
by the automatic video surveillance system. Automatic video surveillance systems are
dangerous sites. Som e practical issues m ust be taken in to account, in order to take
processed and possibly stored by the VS system , as a proof in front of a court of law w ithout leaving any visible trace of the m odification. S or im age data have no o digital
one of such issues. But visual data can be m odified using sophisticated processing t
value as legal proof, since doubt would always exist that they had been intentionally created artificially by computerized techniques su as morphing. Therefore the true ch origin of the data m ust be indicated to use them as legal proof. By data authenticat indicating their true origin.
tam pered with to incrim inate or exculpate the defendant. Besides, the video data ca
m ean here a procedure capable of ensuring that data have not been tam pered w ith
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Image Authentication Techniques
2. AUTOMATIC VISUAL SURVEILLANCE SYSTEM
Automatic Visual Surveillance system is a self monitoring system which consists of a video camera unit, central unit and transmission networks.(figure)
2.1 Automatic Visual Surveillance System
A pool of digital cameras is in charge of frame the scene of interest and sent
corresponding video sequence to central unit. The central unit is in charge of analyz
the sequence and generating an alarm w henever a suspicious situation is detected. provider, the police departm ent or a security guard unit. Som ewhere in the system
unit also transm its the video sequences to an intervention centre such as security service
video sequence or som e part of it m ay be stored and w hen needed the stored seque to be legally credible, som e m eans m ust be envisaged to detect content tam pering reliably trace back to the data origin
can be used as a proof in front of court . If the stored digital video sequences have of law
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Image Authentication Techniques
3. AUTHENTICATION TECHNIQUES
Authentication techniques are perform ed on visual data to indicate that the data is
forgery; they should dam age visual quality of the video data. At the sam e tim e, th not
techniques must indicate the malicious modifications include removal or insertion o
certain fram es, change of faces of individual, tim e and background etc. Only a prope for authenticating video data. They are as follows
authenticated video data has got the value as legal proof. There are two m ajor techni
3.1 Cryptographic Data Authentication
It is a s tra ig h t fo rw a rd w a y to p ro v id e v id e o a u thnean tic a tio nthrough the joint m e ly , use of asymmetric key encryption and the digital Hash function.
Cameras calculate a digital summary (digest) of the video by means of hash functio
Then they encrypt the digest with their private key, thus obtaining a signed digest which
is transm itted to the central unit together w ith acquired sequences. This digest is us public key of the camera.
prove data integrity or to trace back to their origin. Signed digest can only read by u
3.2 Watermarking- based authentication
W aterm arking data authentication is the m odern approach to authenticate visual da imperceptibly embedding a digital watermark signal on the data. Digital w aterm arking is the art and science of em bedding copyright inform ation in the original files. The inform ation em bedded is called ‘waterm arks Digital waterm arks are ‘. difficult to rem ove without noticeably degrading the content and are a covert m ean situation where copyright fails to provide robustness.
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Image Authentication Techniques
4. CRYPTOGRAPHY
M ounting concern over the new threats to privacy and security has lead pread s to wide mainly two functions
adoption of cryptography. Cryptography is the science of transform ing docum ents. I
♦ Encryption ♦ Decryption
The purpose of encryption is to render a docum ent unreadable by all except those w
authorize to read it. Cryptographers refer to the content of the original docum ent as p The key is a randomly selected string of numbers.
text. Plain text is converted in to cipher form using an algorithm and a variable or ke
PLAIN TEXT
CIPHER TEXT
ENCRYPTION KEY
ENCRPTION ALGORITHEM
DECRYPTION KEY
DECRYPTION ALGORITHEM
CIPHER TEXT
PLAIN TEXT
4.1 Encryption and Decryption
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Only after decoding the cipher text using the key the contentdocum ent is revealed the of to the common people. Encryption schemes are classified in to :
1. Symmetric encryption In which the same key is used to both encode and decode the document. 2. Public key or asymmetric encryption
It requires a pair of keys: one for encrypting the plain text and the other for decrypting the same pair
the cipher text. A file encrypted w ith one key of a pair can be decrypted w ith other k
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Image Authentication Techniques
5. CRYPTOGRAPHIC DATA AUTHENTICATION
To authenticate visual data each video cam era is assigned a different public or priva key private key of any particular camera can be decrypted with its own public key. This property is used to provide center authentication that is to trace back to origin of the true the data.
pair, with private key hardwired within the cameras. A document encrypted with the
5.1 Cryptogarphic Method
Before sending the video sequence to the central unit, cameras calculate a digital
sum m aryor digest of the video by m eans of a proper hash function. The digest is the
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encrypted with their private key. Encryption is done by considering the digitized val the brightness of each pixel. Digital signal is a sequence ofzeros and ones and it is
encrypted with the private key using a proper algorithm . The signed digest thus obt is then transmitted to the central unit together with the acquired visual sequence. Later the signal digest is used to prove data integr to trace back to their origin. The ity or
signed digest is read using the public key of the cam era which produce the video an same hash function.
check if it corresponds to the digest derived from the decrypted video content using
Any m anipulation the data w ill change the calculated im age digest derived from the of
decrypted data. Any discrepancy between the decrypted digest and calculated imag data is genuine. Value of the visual data can be added by tying each fram e to the particular label of of creation of each frame. Any modification of either the date time could be easily or revealed since it would change the locally calculated image digest.
digest indicate that the data has been tam pered, w ith identical digest indicates that
instant the fram e has been produced yet. This can be achieved by printing date and
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5.1 DRAWBACKS OF CRYPTOGRAPHIC AUTHENTICATION
Even though cryptographic data authentication is highly resistant to content tam per suffers from few drawbacks. They are as follows: 1.Knowledge of private key If the manipulatorknows the private key of the camera, he can change the digest to a thing is very small because the private key is hardwired within the camera. 2.Impossible to distinguish between malicious and innocuous modification It is difficult to distinguish between malicious and innocuous manipulations if cryptography is used. Innocuous modifications include compression of the video
involve the m odifications he had m ade on the actual sequence. But the possibility o
sequences. These m odifications are usual ly perform ed by the central unit w hereas diges correspondence between the digest and data would be lost. 3. High requirements of video camera
is calculated on the basis of the uncom pressed data by the cam era. So on com press
To avoid the above discussed problem , the video cam era should perform the com pres high computation as storage requirements. 4. Delay in transmission Digest calculations and encryption introduces a delay in transmission of video
of the video sequences prior to digest calculation. This requires the video cam era to
documents. This is harmful in system where the timely generation of alarm is critica
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5. Protecting privacy is difficult calculated digest.
A part of the program cannot be rem oved for privacy reasons since it will alte
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6. WATERMARKING
A digital waterm ark is a signal that is im perceptibly em beddeddigital data. This within about the host data. Digital w aterm ark is a signal which added to a docum ent to authenticate it and to p the ow nership. A com m only encountered w aterm ark is the logo m ost television digital
signal can be detected or extracted by m eans of com putations to m ake som e assert
channels display on the top of the television screen. Not only does it advertise the c recording. Watermark task consists of two main steps
but also provides the legal benefit of having a source signature persist during video
1. W aterm ark casting:-in w hich the signal represented by the w aterm ark is transm it o v e r th e c h a n n e l, th a t is in w a te rm a rk c a s tin g a n e n c o d etakesca host image r fu n tio n ‘f’ and a watermark ‘w’ and generate a new image Fw= (f, w)
2. Watermark detection:-in which the signal is received and extracted from possibly corrupted image.
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6.1 CLASSIFICATION OF WATERMARKING AUTHENTICATION SCHEMS
The characteristics of waterm arking system largely depend on its application scenar
For instant copy w rite protection application require that the w aterm ark is robust ag transform ation of host docum ent. Tw o approaches for w aterm arking data authe ntication are possible: 1. Fragile watermarking 2. Robust watermarking
m ost com m on data m anipulation,ie its presents can still be detected after nondestru
Fragile waterm arking refers to the case w here w aterm ark inserted w ithin the data is is taken as evidence that data has been tam pered w ith, whereas the inform ation co within data used to demonstrate data origin
or altered as soon as host data undergoes any m odification. W aterm ark loss or alter
In case of robust w aterm arking a sum m ary of the candidate fram e or video sequenc also with the summary. To prove data integrity the information conveyed by the mismatch is taken as an evidence of data tampering. The capability to localize the manipulation will depend on the summary of which is embedded in to the image.
com puted and is inserted w ithin video sequence. Inform ation about the data origin i the
w aterm ark is recovered and com pared w ith the actual content of the sequence. The
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WATERMARKING
FRAGILE WATREMARKING
ROBUST WATERMARKIN G
INVISIBLE WATERMARKIN G
VISIBLE WATERMARKING
DUAL WATERMARKIN G
6.1 Types of Watermarking 6.1.1 ROBUST VERSUS FRAGILE WATERMARK
Sem i fragile w aterm ark is m ore m ature than robust waterm arking. Tam per localizat easier in fragile watermarking but it is difficult to distinguish between malicious and innocuous manipulations.
Im age authentication by m eans of robust waterm arking is very prom ising w ith regar technique depends on the number of bits that can be hidden in to the image.
the distinction betw een m alicious and innocuous m anipulations. The robustness of s
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6.2 REQIREMENTS OF WATERMARKING BASED VS DATA AUTHENTICATION
In order to highlight the peculiarities of VS data authentication. Let us consider the m common requirements for watermarking authentication techniques. 1. The authentication technique not deteriorate the visual quality of data quality. m ust acquired to visual data. 3. The authentication technique should not consider innocuous m anipulation, e.g., im age compression and zooming, as valid authentication attacks. 4. It should be difficult for unauthorized person to forge an authenticated image. persons. 6. The authentication checking procedure should localize data tampering.
2. The authentication technique should be able to identify any unauthorized process
5. The authentication checking procedure should be easily performed by authorized
By considering particular cases the requirem ent for the authentication of VS data ar following.
6.2.1 THE INVISIBILITY CONSTRAINT
The requirem ent on the deterioration ofvisual quality of authenticated data is usuall the referred to us as invisibility constraint. The authentication technique m ust not deteriorate the visual quality of data. In this case how ever this is not crucial issue since VS do not exhibit a com parable that of quality
visual data used in a m edia. VS data acquired by inexpensive, low quality devices. V
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analysis w ould possibly be carried out in a low court will focus on the sem antic conten of the image, rather than on their visual quality.
6.2.2 MALICIOUS VERSUS INNOCUOS MANIPULATIONS
The authentication technique should be able to identify any nonauthorized or m alicious consider innocuous manipulation Eg: Image compression or Zooming, as valid authentication techniques. W hen data com pression is done in central unit the authentication is perform ed before com pression and m ust survive it. To satisfy privacy com plaints, som e processing is which are unimportant on the law point of view. This kind of processing as to be considered as m alicious w hen inform ation that is im portant for a court law is rem ov A solution to this problem is offered by authe ntication techniques capable of localizing to decide if it is malicious of innocuous.
processing occurred to the visual data. Besides the authentication technique should
on the authenticated video, before it is stored. E.g. for obscuring the faces of person
considered as innocuous. On the other side, the same processing procedure as to be
m anipulations. Once the m odification is precisely localized, it w ill be up to the court
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7. WATERMARKING ALGORITHM
A watermarking algorithm for VS data authentication based on semi-fragile watermarking of each frame of the video sequenceis described in this section. The various steps for the watermarking process are as follows.
7.1 WATERMARK GENERATION AND EMBEDDING
Watermark generation aims at producing a binary or ternary watermark W(X) using cam era that has captured the im age. The block diagram of w aterm ark generation a embedding is shown below.
digital key K and host im age f(x). waterm ark key corresponds to the im age owner o The
In the proposed m ethod as indicating in the figure the waterm ark generation by usin pseudo random number generator and appropriate thresholding.
The w aterm ark key used for waterm arking a specific fram e in the sequence is com p provides the advantage of producing frame–dependent watermarks. To perform authenticity check, the detection should first know the fram e num ber in sequence which is always zero. Watermark embedding is performed by altering all the pixels of the original frame according to the following formula. Fw(x) = f(x) if w(x) = 0
of the cam era id and fram e num ber. Generating the w aterm ark key using fram e num
In this case, fram e rem oval or fram e substitution can be easily detected as non auth
g 1 (f(x ) , n (x ))if w(x) =-1
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g2 (f(x), n(x) if w(x) =1 Where g1g2 are suitably designed function based on x. n(x) denotes a function that depends on neighborhood of x.
The function g1g2 are called em bedding function and are selected so as to detect th watermarked image fw(x), produces the watermark w(x). D (fw(x), N(x)) = w(x)
inverse detection function. D (fw(x), n(x)). The detection function, w hen applied to t
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7.2 WATERMARK DETECTION
In the w aterm ark detection procedure, the detector generates first the water m ark f the frame number are needed.
fram e to be checked. To do so, the id num ber of cam era that produce the sequence
7.2 Watermark Detection
watermarked image a detection image d(x) is produced. d(x) = D (fw(x), n(x)) Now we frame the false detection image given by
A detection function D is defined such that by applying the detection function to the
E w (x ) = 1if w(x) 0 and w(x) d(x) 0 otherwise
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The false detection image has value 1 if a watermarked pixel is falsely detected and otherw ise. The w aterm arked detection ratio is given by the ratiocorrectly detected of the pixel to the sum of the watermarked pixels in the image.
7.3 AUTHENTICATION CHECK
Authentication check is a tw o level process. A first level decision on im age authentic is taken by com paring the w aterm ark detection of the text im age w ith a pre specified threshold T.
If the first level decision test indicates that the im age is som ehow altered but authe second level decision test should be performThis test indicates whether the ed.
alternations m ade on the im age are concentrated in certain regions (Malicious tam p or one spread on the image (innocuous alternations).
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8. OTHER APPLICATIONS
1. To protect the intellectual property right of a music publisher who distributes music scores over digital media.
Digital piracy is a serious concern to the musical industry.Customers receive easily. By using image score watermarking we can prevent this. 1. It canbe used for everything from sending e-m ail and storing m edical record and legal contracts to conducting on-line transactions.
m usic in digital data form at and such data can be pirated and redistributed ve
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9. ADVANTATGES
1. Robustness to high quality lossy image compression. 2. Automatic discrimination between malicious and innocuous manipulations. 3. Controllable visualdeterioration of the VS sequence by varying the watermark embedding power. 4. Watermark embedding and detection can be performed in real time for digital data.
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10. DISADVANTAGES
1. Frame independent watermark can be easily found by comparative analysis of all image sequence frames and then could be easily added again to fake frames. 2. The detector should know the fram e num ber in order to perform authenticity che
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.
11. CONCLUSION
In these modern eras, visual surveillance system finds application in almost all fields ranging from com m ercial to defense. The video data acquired system are form ing by VS vital evidence for several legal situations. So for such situations, the importance of authenticating their content is very high. Cryptography and watermarking based authenticating techniques are quite safe and efficient for this and they are likely purpose to remain for quite for some while.
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12. REFERENCES
1. C. Ragazoni, G.Fabri, “Image Authentication Techniques for VS”, Proceedings IEEE, October 2001.
2. “Digital Watermarking for protecting piracy Electronics for you, January 2003. ”, 3. “Encryption wars”, IEEE Spectrum, April 2000. 4. M.M.Yeung and F.Mintzer “A watermark for digital image” IEEE Spectrum, April 2002. 5. www.ctr.columbia.edu
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