Near-Optimal Watermark Estimation and Its Countermeasure: Antidisclosure Watermark for Multiple Watermark Embedding

Robustness is a critical requirement for a watermarking scheme to be practical. Current watermarking methods usually claim a certain degree of robustness against those attacks that aim to destroy a hidden watermark at the expense of degrading the quality of the media data. However, there exist watermark-estimation attack (WEA), such as the collusion attack, which can remove watermarks while making the attacked data further transparent to its original. Another kind of attack is the copy attack, which can cause protocol ambiguity within a watermarking system. The aim of this paper is to deal with the WEA, which is clever at disclosing hidden information for unauthorized purposes. To this end, we begin by gaining insight into the WEA, leading to formal definitions of optimal watermark estimation and near-perfect cover data recovery. Subject to these definitions, a new content-dependent watermark (CDW) is proposed to deal with watermark-estimation attack. Mathematical analyses and experimental results consistently verify the effectiveness of the proposed watermark estimation and recovery algorithm, and the proposed content-dependent watermark. To our knowledge, this anti-disclosure watermark is the first work that can give those multiple-redundant watermark embedding approaches resistance to both collusion and copy attacks