Robust Local Watermarking on Salient Image Areas

Abstract

Digital content services and tools have spread all over the world creating an acute need for robust copyright protection and ownership management systems. Robust watermarking technology is playing a crucial roll in these systems developments. This paper reports a robust technique for digital image watermarking. Salient image areas extracted from the pixel domain are used to embed local watermarks in the frequency domain. Relevant image corners are first extracted using well- established scale-space theories for edge and corner detection. Fairly small areas around each corner are used to insert the watermark. The objective is to achieve robustness against local and global geometric transformations as well as conventional image processing attacks while keeping the computational cost low. The DFT is applied on the discrete polar coordinates over asymmetric grids defined on uniform angles and nonuniform radii. The objective is to keep the rotation invariance property of the DFT magnitude while avoiding numerical and interpolation errors on the radii axis. A blind watermark detection process based on statistical correlation is used. Several experiments to validate the robustness of the proposed approach were conducted and are reported in the paper.