Rotation and scale invariant image watermarking based on polar harmonic transforms

Geometric attacks such as rotation and scale can destroy the synchronization of watermarking, designing a geometric-distortion resilient watermarking is currently a challenging work. In this paper, we propose a robust image watermarking technique based on polar harmonic transforms (PHTs) which are defined in a circle domain. The watermarking embedding process includes three principal steps: Firstly, we explicitly exploit invariant properties of PHTs' moments to compute orthogonal moment features. Next, according to the order and repetition of PHTs' moments, steady moments those are not sensitive to geometric attacks are picked out. Finally, watermark embedding is performed through quantization modulation on the selected steady moments, and the watermarked image is reconstructed by combining the original and the compensating image acquired from unmodulated and modulated PHTs' moments, respectively. Experimental results show that the proposed watermarking approach is robust to both geometric distortions (rotation and scaling) and general signal processing attacks (Gaussian filtering, median filtering, average filtering, Gaussian noise, salt & pepper noise, speckle noise, JPEG compression, etc.) and outperforms state-of-the-art watermarking methods.