Hybrid robust watermarking resistant against copy attack

Three major aspects in the protection of digital documents have been pointed out, each of them with different requirements: first copyright protection, protecting ownership and usage rights; secondly tamper-proofing, aiming at checking document integrity; and thirdly authentication, the purpose of which is to check the authenticity of a document. While robust watermarks are typically used for copyright protection, fragile or semi-fragile watermarks are proposed to solve tamper-proofing and authentication. However both concepts are generally proposed separately; further, most of robust watermarking schemes are vulnerable to the copy attack, which allows copying a watermark from one document to another without need for any apriori knowledge [4]. In this paper we propose an hybrid watermarking method which joins a highly robust watermark with a fragile/semi-fragile watermark, combining copyright protection and tamper-proofing, and being at the same time resistant against copy attack; the fragile information is inserted in a way which fully preserves the robust part.