Combining digital watermarks and collusion secure fingerprints for digital images
Digital watermarking is the enabling technology to prove ownership on copyrighted material, detect originators of illegally made copies, monitor the usage of the copyrighted multimedia data, and analyze the spread spectrum of the data over networks and servers. Embedding of unique customer identification as a watermark into data is called fingerprinting to identify illegal copies of documents. Basically, watermarks embedded into multimedia data for enforcing copyrights must uniquely identify the data and must be difficult to remove, even after various media transformation processes. Digital fingerprinting raises the additional problem that we produce different copies for each customer. Attackers can compare several fingerprinted copies to find and destroy the embedded identification string by altering the data in those places where a difference was detected. In our paper we present a technology for combining a collusion-secure fingerprinting scheme based on finite geome tries and a watermarking mechanism with special marking points for digital images. The only marking positions the pirates cannot detect are those positions which contain the same letter in all the compared documents, called intersection of different fingerprints. The proposed technology for a maximal number d of pirates, puts enough information in the intersection of up to d fingerprints to uniquely identify all the pirates.