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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 Technology.
DHANYA K SUDHEESH
SEMINAR GUIDE
Date:
Science and Engineering of Cochin University of
Dr. David Peter S
Head of the Department
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 people
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 are
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.
9.
10.
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
WATERMARKING
9.1 CLASSIFICATION OF WATERMARKING
AUTHENTICATION SCHEMS
9.2 REQIREMENTS OF WATERMARKING BASED
VS DATA AUTHENTICATION
WATERMARKING ALGORITHM
PAGE NO
iii
v
vi
1
2
3
4
8
10
11
13
15
10.1 WATERMARK GENERATION AND EMBEDDING
10.2 WATERMARK DETECTION
10.3 AUTHENTICATION CHECK
15
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
Automatic Visual Surveillance System
Encryption and Decryption
Cryptogarphic Method
Types of Watermarking
Watermark Detection
PAGE NO
2
4
6
12
17
List of Symbols, Abbreviations and Nomenclature
SI. NO.
1
2
ITEM
AVSS
VS
DEFINITION
Automatic Visual Surveillance System
Visual Surveillance
Image Authentication Techniques
1. INTRODUCTION
This paper explores the various techniques used to authenticate the visual data recorded
by the automatic video surveillance system. Automatic video surveillance systems are
used for continuous and effective monitoring and reliable control of remote and
dangerous sites. Some practical issues must be taken in to account, in order to take full
advantage of the potentiality of VS system. The validity of visual data acquired,
processed and possibly stored by the VS system, as a proof in front of a court of law is
one of such issues. But visual data can be modified using sophisticated processing tools
without leaving any visible trace of the modification. So digital or image data have no
value as legal proof, since doubt would always exist that they had been intentionally
tampered with to incriminate or exculpate the defendant. Besides, the video data can be
created artificially by computerized techniques such as morphing. Therefore the true
origin of the data must be indicated to use them as legal proof. By data authentication we
mean here a procedure capable of ensuring that data have not been tampered with and of
indicating their true origin.
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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 analyzing
the sequence and generating an alarm whenever a suspicious situation is detected. Central
unit also transmits the video sequences to an intervention centre such as security service
provider, the police department or a security guard unit. Somewhere in the system the
video sequence or some part of it may be stored and when needed the stored sequence
can be used as a proof in front of court of law. If the stored digital video sequences have
to be legally credible, some means must be envisaged to detect content tampering and
reliably trace back to the data origin
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Image Authentication Techniques
3. AUTHENTICATION TECHNIQUES
Authentication techniques are performed on visual data to indicate that the data is not a
forgery; they should not damage visual quality of the video data. At the same time, these
techniques must indicate the malicious modifications include removal or insertion of
certain frames, change of faces of individual, time and background etc. Only a properly
authenticated video data has got the value as legal proof. There are two major techniques
for authenticating video data. They are as follows
3.1 Cryptographic Data Authentication
It is a straight forward way to provide video authentication, namely through the joint
use of asymmetric key encryption and the digital Hash function.
Cameras calculate a digital summary (digest) of the video by means of hash function.
Then they encrypt the digest with their private key, thus obtaining a signed digest which
is transmitted to the central unit together with acquired sequences. This digest is used to
prove data integrity or to trace back to their origin. Signed digest can only read by using
public key of the camera.
3.2 Watermarking- based authentication
Watermarking data authentication is the modern approach to authenticate visual data by
imperceptibly embedding a digital watermark signal on the data.
Digital watermarking is the art and science of embedding copyright information in the
original files. The information embedded is called ‘watermarks ‘. Digital watermarks are
difficult to remove without noticeably degrading the content and are a covert means in
situation where copyright fails to provide robustness.
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Image Authentication Techniques
4. CRYPTOGRAPHY
Mounting concern over the new threats to privacy and security has lead to wide spread
adoption of cryptography. Cryptography is the science of transforming documents. It has
mainly two functions
♦ Encryption
♦ Decryption
The purpose of encryption is to render a document unreadable by all except those who
authorize to read it. Cryptographers refer to the content of the original document as plain
text. Plain text is converted in to cipher form using an algorithm and a variable or key.
The key is a randomly selected string of numbers.
PLAINTEXT CIPHER TEXT
ENCRYPTIONKEY
ENCRPTIONALGORITHEM
CIPHERTEXT
DECRYPTIONKEY DECRYPTION
ALGORITHEM
PLAIN TEXT
4.1 Encryption and Decryption
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Image Authentication Techniques
Only after decoding the cipher text using the key the content of the document is revealed
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 cipher text. A file encrypted with one key of a pair can be decrypted with other key of
the same pair
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Image Authentication Techniques
5. CRYPTOGRAPHIC DATA AUTHENTICATION
To authenticate visual data each video camera is assigned a different public or private key
pair, with private key hardwired within the cameras. A document encrypted with the
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 the true origin of
the data.
5.1 Cryptogarphic Method
Before sending the video sequence to the central unit, cameras calculate a digital
summary or digest of the video by means of a proper hash function. The digest is then
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Image Authentication Techniquesencrypted with their private key. Encryption is done by considering the digitized value of
the brightness of each pixel. Digital signal is a sequence of zeros and ones and it is
encrypted with the private key using a proper algorithm. The signed digest thus obtained
is then transmitted to the central unit together with the acquired visual sequence.
Later the signal digest is used to prove data integrity or to trace back to their origin. The
signed digest is read using the public key of the camera which produce the video and
check if it corresponds to the digest derived from the decrypted video content using the
same hash function.
Any manipulation of the data will change the calculated image digest derived from the
decrypted data. Any discrepancy between the decrypted digest and calculated image
digest indicate that the data has been tampered, with identical digest indicates that the
data is genuine.
Value of the visual data can be added by tying each frame to the particular label of the
instant the frame has been produced yet. This can be achieved by printing date and time
of creation of each frame. Any modification of either the date or time could be easily
revealed since it would change the locally calculated image digest.
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Image Authentication Techniques
5.1 DRAWBACKS OF CRYPTOGRAPHIC AUTHENTICATION
Even though cryptographic data authentication is highly resistant to content tampering, it
suffers from few drawbacks. They are as follows:
1.Knowledge of private key
If the manipulator knows the private key of the camera, he can change the digest to
involve the modifications he had made on the actual sequence. But the possibility of such
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
sequences. These modifications are usually performed by the central unit whereas digest
is calculated on the basis of the uncompressed data by the camera. So on compression the
correspondence between the digest and data would be lost.
3. High requirements of video camera
To avoid the above discussed problem, the video camera should perform the compression
of the video sequences prior to digest calculation. This requires the video camera to have
high computation as storage requirements.
4. Delay in transmission
Digest calculations and encryption introduces a delay in transmission of video
documents. This is harmful in system where the timely generation of alarm is critical.
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Image Authentication Techniques
5. Protecting privacy is difficult
A part of the program cannot be removed for privacy reasons since it will alter the
calculated digest.
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Image Authentication Techniques
6. WATERMARKING
A digital watermark is a signal that is imperceptibly embedded within digital data. This
signal can be detected or extracted by means of computations to make some assertions
about the host data.
Digital watermark is a signal which added to a document to authenticate it and to prove
the ownership. A commonly encountered digital watermark is the logo most television
channels display on the top of the television screen. Not only does it advertise the channel
but also provides the legal benefit of having a source signature persist during video
recording. Watermark task consists of two main steps
1. Watermark casting:-in which the signal represented by the watermark is transmitted
over the channel, that is in watermark casting an encoder function
‘f’ and a watermark ‘w’ and generate a new image
takes a host image
Fw= (f, w)
2. Watermark detection:-in which the signal is received and extracted from possibly
corrupted image.
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Image Authentication Techniques
6.1 CLASSIFICATION OF WATERMARKING
AUTHENTICATION SCHEMS
The characteristics of watermarking system largely depend on its application scenario.
For instant copy write protection application require that the watermark is robust against
most common data manipulation,ie its presents can still be detected after nondestructive
transformation of host document. Two approaches for watermarking data authentication
are possible:
1. Fragile watermarking
2. Robust watermarking
Fragile watermarking refers to the case where watermark inserted within the data is lost
or altered as soon as host data undergoes any modification. Watermark loss or alternation
is taken as evidence that data has been tampered with, whereas the information contained
within data used to demonstrate data origin
In case of robust watermarking a summary of the candidate frame or video sequence is
computed and is inserted within the video sequence. Information about the data origin is
also with the summary. To prove data integrity the information conveyed by the
watermark is recovered and compared with the actual content of the sequence. Their
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.
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Image Authentication Techniques
WATERMARKING
FRAGILEWATREMARKING
ROBUSTWATERMARKING
INVISIBLEWATERMARKIN
G
VISIBLEWATERMARKING
DUALWATERMARKIN
G
6.1 Types of Watermarking
6.1.1 ROBUST VERSUS FRAGILE WATERMARK
Semi fragile watermark is more mature than robust watermarking. Tamper localization is
easier in fragile watermarking but it is difficult to distinguish between malicious and
innocuous manipulations.
Image authentication by means of robust watermarking is very promising with regards to
the distinction between malicious and innocuous manipulations. The robustness of such
technique depends on the number of bits that can be hidden in to the image.
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Image Authentication Techniques
6.2 REQIREMENTS OF WATERMARKING BASED VS DATA
AUTHENTICATION
In order to highlight the peculiarities of VS data authentication. Let us consider the most
common requirements for watermarking authentication techniques.
1. The authentication technique must not deteriorate the visual quality of data quality.
2. The authentication technique should be able to identify any unauthorized processing
acquired to visual data.
3. The authentication technique should not consider innocuous manipulation, e.g., image
compression and zooming, as valid authentication attacks.
4. It should be difficult for unauthorized person to forge an authenticated image.
5. The authentication checking procedure should be easily performed by authorized
persons.
6. The authentication checking procedure should localize data tampering.
By considering particular cases the requirement for the authentication of VS data are
following.
6.2.1 THE INVISIBILITY CONSTRAINT
The requirement on the deterioration of the visual quality of authenticated data is usually
referred to us as invisibility constraint.
The authentication technique must not deteriorate the visual quality of data. In this VS
case however this is not crucial issue since VS do not exhibit a quality comparable that of
visual data used in a media. VS data acquired by inexpensive, low quality devices. Visual
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Image Authentication Techniquesanalysis would possibly be carried out in a low court will focus on the semantic content
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 malicious
processing occurred to the visual data. Besides the authentication technique should not
consider innocuous manipulation Eg: Image compression or Zooming, as valid
authentication techniques.
When data compression is done in central unit the authentication is performed before
compression and must survive it. To satisfy privacy complaints, some processing is done
on the authenticated video, before it is stored. E.g. for obscuring the faces of persons
which are unimportant on the law point of view. This kind of processing as to be
considered as innocuous. On the other side, the same processing procedure as to be
considered as malicious when information that is important for a court law is removed.
A solution to this problem is offered by authentication techniques capable of localizing
manipulations. Once the modification is precisely localized, it will be up to the court law
to decide if it is malicious of innocuous.
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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 sequence is 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 a
digital key K and host image f(x). The watermark key corresponds to the image owner or
camera that has captured the image. The block diagram of watermark generation and
embedding is shown below.
In the proposed method as indicating in the figure the watermark generation by using a
pseudo random number generator and appropriate thresholding.
The watermark key used for watermarking a specific frame in the sequence is composed
of the camera id and frame number. Generating the watermark key using frame number
provides the advantage of producing frame–dependent watermarks.
In this case, frame removal or frame substitution can be easily detected as non authentic.
To perform authenticity check, the detection should first know the frame number in the
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)
g1 (f(x), n(x))
Division of Computer Engineering
if w(x) = 0
if w(x) =-1
15
Image Authentication Techniquesg2 (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 embedding function and are selected so as to detect the
inverse detection function. D (fw(x), n(x)). The detection function, when applied to the
watermarked image fw(x), produces the watermark w(x).
D (fw(x), N(x)) = w(x)
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Image Authentication Techniques
7.2 WATERMARK DETECTION
In the watermark detection procedure, the detector generates first the water mark for each
frame to be checked. To do so, the id number of camera that produce the sequence and
the frame number are needed.
7.2 Watermark Detection
A detection function D is defined such that by applying the detection function to the
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
Ew(x) = 1if w(x) 0 and w(x) d(x)
0 otherwise
Division of Computer Engineering 17
Image Authentication TechniquesThe false detection image has value 1 if a watermarked pixel is falsely detected and 0
otherwise. The watermarked detection ratio is given by the ratio of the correctly detected
pixel to the sum of the watermarked pixels in the image.
7.3 AUTHENTICATION CHECK
Authentication check is a two level process. A first level decision on image authenticity
is taken by comparing the watermark detection of the text image with a pre specified
threshold T.
If the first level decision test indicates that the image is somehow altered but authentic, a
second level decision test should be performed. This test indicates whether the
alternations made on the image are concentrated in certain regions (Malicious tampering)
or one spread on the image (innocuous alternations).
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Image Authentication Techniques
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
music in digital data format and such data can be pirated and redistributed very
easily. By using image score watermarking we can prevent this.
1. It can be used for everything from sending e-mail and storing medical records
and legal contracts to conducting on-line transactions.
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Image Authentication Techniques
9. ADVANTATGES
1. Robustness to high quality lossy image compression.
2. Automatic discrimination between malicious and innocuous manipulations.
3. Controllable visual deterioration 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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Image Authentication Techniques
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 frame number in order to perform authenticity check
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Image Authentication Techniques
.
11. CONCLUSION
In these modern eras, visual surveillance system finds application in almost all fields,
ranging from commercial to defense. The video data acquired by VS system are forming
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 purpose and they are likely
to remain for quite for some while.
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Image Authentication Techniques
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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