Image analysis – Applications
Reexamination Certificate
2000-09-06
2004-03-02
Patel, Jayanti K. (Department: 2621)
Image analysis
Applications
C380S201000
Reexamination Certificate
active
06700993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a digital watermark detection technique. In particular, the present invention relates to a system, method and computer program product for an on-line digital watermark detection, wherein a user terminal authenticates watermark information such as copy protect embedded in images, by using a key generated by a detection center for extracting and encrypting the embedded information and an authentication key generated by the detection center.
2. Description of the Prior Art
As digital media containing images or video images become popular, there arises a need for such a system wherein information identifying an author of a medium is added to the medium and the information is read out as occasion demands.
For example, information concerning permission of duplication is added to a media and a medium playback device is provided with a function of reading and writing this information to prevent illegal duplications.
If in this case the information concerning the permission of duplication is inseparable from the medium itself, the illegal duplications become possible by falsifying the information.
Therefore, the information added to the images must be inseparable from the images.
As one of techniques for solving this problem, there is a digital watermark technique. For example, a digital watermark technique for a still picture” is a technique for obtaining a watermarked image with some additional information embedded therein by adding an alteration of such a degree as not to be recognized by human vision to an original image transformed to digital data.
By digital watermark embedding, information is embedded in the image itself without greatly hampering the appearance.
There is an example proposed by Ingemar Cox et al. disclosed in JP9-191394 A (1997) and a paper “Secure spread spectrum watermarking for multimedia,” IEEE TRANSACTIONS ON IMAGE PROCESSING, vol. 6, No. 12, December, 1997.
In this scheme, an original image is transformed to data (spectra) of the signal domain by using Fourier transform and discrete cosine transform, and noise generated by a pseudo random number is added to a portion considered to be visually important in the spectra in order to embed information.
Furthermore, in Reference 1 by J. R. Smith et al., “Modulation and information hiding in images,” First workshop on information hiding, Lecture notes in computer science vol. 1174, July 1996, there is shown such a model that digital watermark embedding and detection are grasped as modulation and demodulation in communication.
Many digital watermark schemes currently proposed can be described by this model or a simple modification of this model. Hereafter, the outline of the model will be described.
By the way, in digital watermark schemes, there are schemes using the original image in detection and schemes which do not use the original image in detection.
A system in the present invention is intended for the latter cited schemes. Hereafter, therefore, the system of the present invention will be described as to the digital watermark scheme conducting detection which does not require the original image.
It is now assumed that information V is to be embedded in an image S, in the digital watermark scheme using detection which does not require the original image.
In this case, for data f(S) obtained by transforming S, a watermarked image S′ satisfying the relation f(S′)=W′×V is generated. As examples of the data f(S), data or a part of data subjected to signal transform such as DCT or Fourier transform, and various statistics such as the moment of the image are considered.
Here, data f(S) is referred to as feature quantity of S. In the case where detection is conducted from the watermarked image S′, W×f(S′) is derived. However, it is necessary that column vectors of W′ are orthogonal. W′ is an inverse matrix of W. In the case where embedded information is V, it is shown by (Equation 1) that the embedded information V is obtained by detection.
W×f
(
S
′)=
W×W′×V=V
(Equation 1)
W′ is a modulation matrix, and W is a demodulation matrix.
For example, in the case where some editing is being conducted for the watermarked image S′, the (Equation 1) is not valid, but it is considered that an Euclidean distance between the embedded information V and W×f(S′) becomes shorter depending upon the degree of editing.
In this case, V is obtained by quantizing W×f(S′). In the case where one bit of the embedded information is 1 or −1, quantization q(X) of a vector X=(x
1
, . . . , xn) is represented by the following (Equation 2).
q
(
X
)=(
x
′
1
,
x
′
2
, . . . ,
x′m
) (Equation 2)
x′i=1 if xi is positive
x′i=−1 otherwise
For executing detection in the digital watermark scheme coming under this model, it is sufficient to know the transform f( ) and the matrix W.
In other words, f( ) and W can be regarded as a key required to detect the digital watermark. In this case, a person who knows f( ) and W can find which portion of the signal domain of the original image is altered to embed the information.
Therefore, it is possible to falsify the watermarked image. Herein, however, falsifying means to alter a watermarked image so that an originally embedded information will not be detected or information different from the originally embedded information will be detected, without greatly degrading the picture quality of the watermarked image.
In a system using a digital watermark, there is demanded sometimes a condition that every user of a digital watermark can know the embedded information.
Hereafter, two approaches considered to satisfy the above described condition will be described.
First, as an example of a first approach, there is a paper written by Matsui et al., “An Application system for Watermark techniques: A protocol for detecting illicit copy images using user's browsing operation”, Encryption and information security symposium, 10, 2. C, January 1998.
In a system proposed by this paper, a digital watermark detection program is distributed to users beforehand, and a user singly executes detection by using this program in order to obtain embedded information.
In the system of Matsui et al., key information required for detection is included in the detection program. In the case where a user has known key information required for detection, the user can perform falsification.
Therefore, supposition that users cannot know key information from the detection program becomes necessary. The fact that a program is secure against analyses conducted by malicious users is represented by an expression that the program has tamper resistance.
As the other approach, there is such a system that a reliable center executes the detection and notifies a user of only a detection result. As its example, there can be mentioned a paper written by Yoshiura et al. “Secure Watermarking System using Public key Cryptography”, The Institute of Electronics, Information and Communication Engineers, Conference of Foundation and Boundary, SA-7-7, September 1997. Even if a center which executes the detection answers an illegal detection result to a user, the user cannot gain an insight, in the system of Yoshiura et al. Therefore, to what extent the center executing the detection is reliable becomes important. Furthermore, in the system of Yoshiura et al., it is conceivable that a user executes a part of detection processing such as the transform to the signal domain. In this case as well, it can be said that the possibility of success of falsification is increased by the user analyzing software possessed by the user.
In systems according to the above described two approaches in which anyone of users of a watermarked image can know embedded information, the security against falsification and reliability of the system can be said to b
Azarian Seyed
Foley & Lardner
Patel Jayanti K.
LandOfFree
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