Ring-shaped digital watermark for rotated and scaled images using random-phase sinusoidal function

Digital watermarking for a still image is considered. A new spatial-domain watermarking method is presented. The method is applicable for rotated and scaled images. A watermark is constructed with a ring-shaped constraint. A sinusoidal function with random phase is used for generating each watermark ring. The method can not only be used for watermark detection in the presence of image rotation, but also for the estimation of the angle rotated, without the need for the original image. A practical method for the construction of such a watermark is described. Results from experiments performed with images, in electronic and printed forms, are provided.