Collusion issue in video watermarking

Security evaluation of released watermarking algorithms has recently become a major concern. In this perspective, it is worth evaluating the importance of the threat of collusion attacks. These attacks combine several watermarked documents to produce unwatermarked content. In video, such a strategy is all the more critical since each individual video frame can be seen as a single watermarked document. Once different weaknesses against collusion attacks have been exhibited, a novel signal coherent watermarking strategy is presented. The goal is to generate a watermark signal coherent with the redundancy of the host video signal, should it be temporal or spatial, so that the embedded watermark is immune against collusion attacks