Countermeasure for collusion attacks against digital watermarking

Customer identification watermarking today is one of the most promising application domains of digital watermarking. It enables to identify individual copies of otherwise indistinguishable digital copies. If done without any precautions, those individual watermarking are vulnerable to a number of specialized attacks based on an attacker collecting more than one individual copy. Fingerprinting algorithms are used to create watermarks robust against these attacks, but the resulting watermarks require a high payload of the watermarking algorithm. As soon as a large number of copies need to be distinguished and more than two copies are available to the attacker, the watermarks are too long to be embedded with current algorithms. We present a novel alternative method to fight attacks aimed at individual customer identification watermarks. This is achieved by modifying the watermarked material in a way collusion attacks produce artifacts which significantly reduce the perceived quality while they do not affect the quality of the individual copies.