An image watermarking scheme to resist generalized geometrical transformations

Most of the watermarking schemes are based on the additive spread-spectrum method since the embedded watermark can resist more serious content distortion and noises. However, they usually fail to be detected when the image undergoes geometrical modifications, such as cropping, rotation, scaling, or even change of the aspect ratio. In this research, we propose a spatial-frequency composite digital image watermarking scheme to make the embedded watermark survive the generalized geometrical transformations. Two watermarks will be embedded, one in the spatial-domain and the other in the frequency-domain of the image. Both embedding processes are based on the spread-spectrum approach. The frequency-domain watermark contains the desired information that will be carried with the host image. The watermark is embedded in the Discrete Fourier Transform (DFT) magnitude so that it is not affected by image translation. The spatial-domain watermarking is used to help recover the image to its original orientation and scale so that the hidden information can then be successfully determined. Experimental results show that the embedded watermark survives generalized geometrical or affine transformations.