A quantization-based digital watermarking robust to geometrical transformations

In this paper, we propose a geometrical transformation resistant digital image watermarking based on quantization, which takes advantage of the rotation, scale and translation invariants of Discrete Fourier Transform, and each watermark bit is embedded into each homocentric circles around the zero frequency term in DFT domain by quantizing the magnitude vector of Fourier spectrum. The embedded sequence can be extracted by "majority principles" without restoring to the original unmarked image. The experimental results show that the watermark is invisible and robust to any combination of geometrical transformations such as rotation, scaling, cropping or translation and common image processing techniques.