The copy attack is an attack on certain
digital watermarking
A digital watermark is a kind of marker covertly embedded in a noise-tolerant signal such as audio, video or image data. It is typically used to identify ownership of the copyright of such signal. "Watermarking" is the process of hiding digital in ...
systems proposed by M. Kutter, S. Voloshynovskiy, and A. Herrige in a paper presented in January, 2000 at the Photonics West
SPIE
SPIE (formerly the Society of Photographic Instrumentation Engineers, later the Society of Photo-Optical Instrumentation Engineers) is an international not-for-profit professional society for optics and photonics technology, founded in 1955. It ...
convention.
In some scenarios, a digital watermark is added to a piece of
media such as an
image
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensio ...
,
film
A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmospher ...
, or
audio clip, to prove its authenticity. If a piece of media were presented and found to lack a watermark, it would be considered suspect. Alternatively, a security system could be devised which would limit a user's ability to manipulate any piece of media which contained a watermark. For instance, a
DVD burner may prohibit making copies of a film which contained a watermark.
The copy attack attempts to thwart the effectiveness of such systems by estimating the watermark given in an originally watermarked piece of media, and then adding that watermark to an un-watermarked piece. In the first scenario listed above, this would allow an attacker to have an inauthentic image be declared authentic, since it contains a watermark. In the second scenario, an attacker could flood the market with content which ordinarily would allow a user to manipulate it as he saw fit, but due to the presence of the watermark, limitations would be imposed. In this way, schemes which sought to limit use of watermarked media may prove to be too unpopular for wide distribution.
In a 2003 paper presented at the
International Conference on Acoustics, Speech, and Signal Processing,
[J. Barr, B. Bradley, and B. Hannigan]
Using Digital Watermarks with Image Signatures to Mitigate the Threat of the Copy Attack
Proceedings of ICASSP, 2003 John Barr, Brett Bradley, and Brett T. Hannigan of
Digimarc describe a way to tie the content of the digital watermark to the underlying image, so that if the watermark were placed into a different image, the
watermark detection system would not authenticate it.
References
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Computer security exploits
Watermarking