Copyright protection of images using robust digital signatures

A method for copyright protection of digital images is presented. Copyright protection is achieved by embedding an "invisible" signal, known as digital signature, in the digital image. Signature casting is performed in the spatial domain by slightly modifying the intensity level of randomly selected image pixels. Signature detection is done by comparing the mean intensity value of the marked pixels against that of the not marked pixels. Statistical hypothesis testing is used for this purpose. The signature can be designed in such a way that it is resistant to JPEG compression and lowpass filtering. This is done by minimizing the energy content of the signature signal in higher frequencies. Experiments on real image data verify the effectiveness of the method.