Effective document fingerprinting

Watermarking digital content is a very common approach leveraged by creators of copyrighted digital data to embed fingerprints into their data. The rationale of such operation is to mark each copy of the data in order to uniquely identify it. These watermarks are embedded in a suitable way to prevent their stripping or modification by users for illegal distribution of the copy. If a copy is illegally distributed by a pirate user (or a set of users referred as coalition) it can be identified by the distributor that can analyze the fingerprint and accuse as traitor the person in charge of that copy. Actions can then be taken against this user, to prevent further illegal distribution. Many approaches have been defined to obtain optimal fingerprinting code based on the wellknown Tardos encoding [6]. In this work, we discuss a simple yet powerful decoding scheme that shows effective in many practical case.