Image analysis – Applications
Reexamination Certificate
1998-11-16
2002-12-10
Mancuso, Joseph (Department: 2623)
Image analysis
Applications
C382S232000, C382S251000, C380S252000, C380S287000, C713S176000
Reexamination Certificate
active
06493457
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic watermarking of datastreams and, in particular, to an imperceptible watermark which is inserted in the compressed domain and can be detected without a reference.
BACKGROUND OF THE INVENTION
Electronic distribution of multimedia content is an important byproduct of the confluence of recent technological advances. Increasing network bandwidth, compression algorithms that preserve audio and video quality while reducing bit rate dramatically, higher density storage devices, and network search engines, when taken together, support network services which are revolutionizing the distribution of music and video.
Content owners naturally wish to maintain control over the distribution of their wares. To effectively protect their intellectual property (IP), an integrated system design is necessary [J. Lacy, D. P. Maher, and J. H. Snyder, “Music on the Internet and the Intellectual Property Protection Problem”,
Proc. International Symposium on Industrial Electronic
, Guimaraes, Portugal, July 1997]. A typical protection system consists of three major building blocks. First, compressed content is stored in a cryptographic container before distribution to users. Second, a flexible licensing mechanism is utilized to answer questions about the trustworthiness of those seeking access to the content. Third, watermarks are embedded in the content in an imperceptible fashion in order that the content can be identified if the cryptographic container has been breached. A secure system design integrates these three components.
An electronic watermark is a data stream inserted into multimedia content. It contains information relevant to the ownership or authorized use of the content. Watermarks typically serve one of three functions: identification of the origin of the content, tracing of illegally distributed copies of the content, and disabling of unauthorized access to the content. No single marking method is best suited to all three functions, both because of complexity and because different functions and marking algorithms are resistant to different kinds of attacks. Any single piece of music or video can therefore be expected to be marked with a variety of different methods.
For copyright identification, every copy of the content can be marked identically, so the watermark needs to be inserted only once prior to distribution. Ideally, detection should not require a reference, because a search engine has no apriori way to identify the work from which it must recover the mark. The watermark particularly needs to be detectable inside an edited work in which the original content may be either shortened or abutted with other works. Not only must the watermark be short enough to be detected in a shortened version of the work, but some means must be provided to synchronize the detection process in order that the watermark can be located in the processed bitstream. Finally, a watermark used for copyright identification must be robust to further processing. Any attempt to remove it, including re-encoding the content, should lead to perceptible distortion.
Transaction identification requires a distinct mark for each transaction. The primary challenge of point-of-sale marking is to move the content through the watermarking engine quickly, meaning that the algorithm used must be of low complexity. One strategy that meets this requirement is to inert the watermark in the compressed domain. Ideally, mark insertion should increase the data rate very little. In contrast to copyright ownership marking, the transaction identification watermark must be robust to collusion attacks.
Disabling access to content is generally best performed by mechanisms other than watermarks. If a watermark is used to disable access to content, the watermark recovery mechanism should be of low complexity. It should not be used as a protection of last resort, however, as disabling access clearly indicates the location of the watermark to anyone who can reverse-engineer the access mechanism.
Watermarks used in conjunction with compression algorithms fall into one of three classes: cleartext (PCM) marking, bitstream marking, and marking integrated with the compression algorithm. Each type has advantages and disadvantages. The intended use of the watermark directly affects the choice of algorithm.
Cleartext marking relies on perceptual methods to imperceptibly embed a data stream in a signal. The model for many cleartext marking algorithms is one in which a signal is injected into a noisy communication channel, where the audio/video signal is the interfering noise [J. Smith, B. Comisky, “Modulation and Information Hiding in Images”,
Proc. First International Information Hiding Workshop
, LNCS 1174, Springer-Verlag, Cambridge, U.K., May/June 1996, pp. 207-226]. Because the channel is so noisy and the mark signal must be imperceptible, the maximum bit rates that are achievable for audio are generally less than 100 bps.
A cleartext mark appears in all processed generations of the work, since by design the marking algorithm is both secure and robust in the face of typical processing. It is therefore well suited to identification of the work. There are two major disadvantages to cleartext marking. First, because such algorithms compute a perceptual model, they tend to be too complex for point-of-sale applications. Second, a potentially significant problem, is that these algorithms are susceptible to advances in the perceptual models used in compression algorithms. Many cleartext marking algorithms have been reported [see, e.g.
Proceedings of the Fourth International Conference on Image Processing
, Santa Barbara Calif., October 1997].
Retrieval mechanisms for cleartext watermarks fall into two classes: reference necessary and reference unnecessary. In either case, the mechanism for mark recovery is generally of high complexity. Furthermore, if means for detecting these watermarks are embedded in a player, an attacker, by reverse engineering the player, may be able to identify and remove the marks. Cleartext watermarks typically should not be used to gate access to content.
Bitstream marking algorithms manipulate the compressed digital bitstream without changing the semantics of the audio or video stream. For example, a data envelope in an MPEG-2 Advanced Audio Coding (AAC) [IS 13818-7 (MPEG-2 Advanced Audio Coding, AAC), M.Bosi, K. Brandenburg, S. Quackenbush, M. Dietz, J. Johnston, J. Herre, H. Fuchs, Y. Oikawa, K. Akagiri, M. Coleman, M. Iwadare, C. Lueck, U. Gbur, B. Teichmann] audio frame could contain a watermark, albeit one which could easily be removed. Bitstream marking is low-complexity, so it can be used to carry transaction information. However these marks cannot survive D/A conversion and are generally not very robust against attack; for example, they are susceptible to collusion attacks. Because the mark signal is unrelated to the media signal, the bit rate that these techniques can support can be as high as the channel rate. This type of mark can be easily extracted by clients and is thus appropriate for gating access to content.
Integrating the marking algorithm with the compression algorithm avoids an ‘arms race’ between marking and compression. Since the perceptual model is available from the workings of the compression algorithm, integrated marking algorithms alter the semantics of the audio or video bitstream, thereby providing resistance to collusion attacks. Depending on the details of the marking algorithm, the mark may survive D/A conversion. An example of this approach is described by F. Hartung and B. Girod in “Digital Watermarking of MPEG-2 Coded Video inthe Bitstream Domain”,
Proc. IEEE ICASSP
, pp. 2621-4, April 1997. The method of Hartung and Girod does not use perceptual techniques.
A watermark which can be recovered without a priori knowledge of the identity of the content could be used by web search mechanisms to flag unauthorized distribution of the content. Since media are compressed on these sites,
Quackenbush Schuyler Reynier
Reibman Amy Ruth
Shur David Hilton
Snyder James H.
AT&T Corp.
Banner & Witcoff , Ltd.
Bhatnagar Anand
Mancuso Joseph
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