Near-perfect cover image recovery anti-multiple watermark embedding approaches

Robustness is a critical requirement for a watermarking scheme to be practical. Especially, in order to resist geometric distortions, a common way is to insert multiple-redundant watermarks locally in the hope that partial watermarks could still be detected. However, there exist watermark-estimation attacks (WEA), such as the collusion attack, that 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 paper proposes an efficient cover data recovery attack, which is more powerful than the conventional collusion attack. 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, an exquisite collusion attack is derived. Experimental results verify the effectiveness of the proposed watermark estimation and recovery algorithm.