Expanding the class of watermark de-synchronization attacks

Geometric transformations whereby the watermark embedder and detector are de-synchronized are known to be one of the most serious threats against any digital watermarking scheme, noticeably against those operating on still images. Despite their importance, only a few classes of geometric attacks are considered in the literature, including global geometric transformations and the random bending attack first introduced by the popular Stirmark software. In this paper we introduce two new classes of de-synchronization attacks (DAs), that extend the class of local geometric attacks so to allow for more powerful and less intrusive attacks. The effectiveness of the new classes of DAs is evaluated from different perspectives including: perceptual intrusiveness and de-synchronization efficacy. This work can be seen as a first step towards the characterization of the whole class of perceptually admissible DAs, which in turn is an essential step towards the development of a new class of watermarking systems that can effectively cope with them. Copyright 2007 ACM.