Spread spectrum watermarking: malicious attacks and counterattacks

Most watermarking methods for images and video have been proposed are based on ideas from spread spectrum radio communications, namely additive embedding of a (signal adaptive or non-adaptive) pseudo-noise watermark pattern, and watermark recovery by correlation. Even methods that are not presented as spread spectrum methods often build on these principles. Recently, some skepticism about the robustness of spread spectrum watermarks has arisen, specifically with the general availability of watermark attack software which claim to render most watermarks undetectable. In fact, spread spectrum watermarks and watermark detectors in their simplest form are vulnerable to a variety of attacks. However, with appropriate modifications to the embedding and extraction methods, spread spectrum methods can be made much more resistant against such attacks. In this paper, we review proposed attacks on spread spectrum watermarks are systematically. Further, modifications for watermark embedding and extraction are presented to avoid and counterattack these attacks. Important ingredients are, for example, to adapt the power spectrum of the watermark to the host signal power spectrum, and to employ an intelligent watermark detector with a block-wise multi-dimensional sliding correlator, which can recover the watermark even in the presence of geometric attacks.