Geometric invariant domain for image watermarking

To enable copyright protection and authentication, robust digital watermark can be embedded into multimedia contents imperceptibly. However, geometric distortions pose a significant threat to robust image watermarking because it can desynchronize the watermark information while preserving the visual quality. To overcome this, we developed an invariant domain with three transforms; Fast Fourier Transform (FFT), Log-Polar Mapping (LPM), and Dual Tree-Complex Wavelet Transform (DT-CWT). Shift invariance is obtained using FFT. Rotation and scaling invariance are achieved by taking the DT-CWT of a LPM output. Unlike most invariant schemes, our method eliminates explicit re-synchronization. The method resists geometric distortions at both global and local scales. It is also robust against JPEG compression and common image processing. In addition, it exploits perceptual masking property of the DT-CWT subbands, and its watermark detection step does not require the cover image. Experiment on a large set of natural images shows the robustness of the new scheme.