Date Added: Apr 2012
Watermarking is a means of tracing the (re-)distribution of content. Before distribution, digital content is modified by applying an imperceptible WaterMark (WM), embedded using a watermarking algorithm. Once an unauthorized copy of the content is found, the WM helps to trace those users who participated in the creation of the copy. This is known as 'Forensic Watermarking'. Reliable tracing requires resilience against attacks that aim to remove the WM. Collusion attacks are a particular threat: multiple users cooperate, and differences between their versions of the content tell them where the WM is located. Coding theory has provided a number of collusion-resistant codes.