Rotation, scaling, and translation-invariant multi-bit watermarking based on log-polar mapping and discrete Fourier transform

This paper proposes an RST-invariant multi-bit watermarking system based on LPM and DFT. This system embeds the watermark in a rotation and translation invariant domain obtained by first acquiring log-polar mapped DFT (LPM-DFT) magnitudes of an image, and then taking the magnitude of the 1-dimensional DFT along the angular axis of these LPM-DFT magnitudes. Neither the original cover image nor a presumed watermark is required during watermark extraction. Scaling invariant is accomplished by a simple search along the log-radius axis. Simulation results indicate that this new system has high robustness against RST distortion and moderate robustness against image compression such as JPEG.