Image content-based watermarking resistant against geometrical distortions

A geometrically robust watermarking scheme was proposed based on image local content, which could resist both image cropping and RST attacks. It first extracts the robust feature points, and then partitions the image into multi circular area. Each area is transformed into PM sub-images, then 2-D DFT is performed and the magnitudes are used as the watermark-embedding domain. Finally the watermark is embedded by modifying the DFT magnitudes using energy modulation. Comparing with Fourier-Mellin transform-based watermarking, its computational cost is reduced as only one 2-D DFT is performed Moreover, the method can overcome the interpolation problem by using PM in the spatial domain because images have a similar scale between neighboring pixels.