Secure hybrid robust watermarking resistant against tampering and copy attack

Digital watermarking appears today as an efficient mean of securing multimedia documents. Several application scenarios in the security of digital watermarking have been pointed out, each of them with different requirements. The three main identified scenarios are: copyright protection, i.e. protecting ownership and usage rights; tamper proofing, aiming at detecting malicious modifications; and authentication, the purpose of which is to check the authenticity of the originator of a document. While robust watermarks, which survive to any change or alteration of the protected documents, are typically used for copyright protection, tamper proofing and authentication generally require fragile or semi-fragile watermarks in order to detect modified or faked documents. Further, most of robust watermarking schemes are vulnerable to the so-called copy attack, where a watermark can be copied from one document to another by any unauthorized person, making these schemes inefficient in all authentication applications. In this paper, we propose a hybrid watermarking method joining a robust and a fragile or semi-fragile watermark, and thus combining copyright protection and tamper proofing. As a result this approach is at the same time resistant against copy attack. In addition, the fragile information is inserted in a way which preserves robustness and reliability of the robust part. The numerous tests and the results obtained according to the Stirmark benchmark demonstrate the superior performance of the proposed approach.