Targeted Dewatermarking of Two SVD-based Image Watermarking Schemes

Targeted Dewatermarking of Two SVD-based Image Watermarking Schemes

Digital watermarking is widely used to verify the authenticity or integrity of multimedia contents, such as images and videos. Recently, the well-known numerical tool called singular value decomposition (SVD) received much attention from the watermarking community. Designers of SVD-based schemes mostly use dewatermarking tools such as Stirmark to prove the robustness of their schemes. Although, these tools are valuable but their distortions usually degrade the quality of watermarked images, and resistance against these distortions does not imply the scheme is secure. Despite of distortions, there are many types of attacks which violate security. There is a kind of attack in which the attacker needs to know the watermarking algorithm to perform the attack. In this paper, two attacks of this kind have been designed against two specific SVD-based watermarking schemes. These attacks try to change the exact spaces where watermarks have been embedded. The experiments show that attacked images by applying our attacks are less distorted than processed images by using Stirmark, so the quality of attacked images is better than processed images in terms of PSNR.;;