RST invariant digital image watermarking: importance of phase information

Based on Fourier-Mellin transform, this paper presents a novel digital image watermarking scheme that is invariant to rotation, scaling, and translation (RST). We embed watermark in the log-polar mappings of Fourier magnitude spectrum of original image, and use the phase information of the original image to rectify the watermark positions. The scheme avoids computing inverse log-polar mapping (ILPM), therefore preserves the image quality. Evaluations demonstrate that the scheme is invariant to rotation and translation, and sufficiently invariant to scaling transformation, and very robust to JPEG compression.