what is a watermarke image

Digital image watermarking is applied today as a popular technique for authentication and copyright protection of image data. Based on global information about the image characteristics, many approaches and commercial solutions embed the watermarking signal as random noise in the whole cover image with the same strength regardless of the local properties of the image. This embedding may lead in practice to visible artifacts specially in the flat regions which are characterized by small variability. In order to decrease these distortions the given watermark strength has to be decreased. This, however, reduces drastically the robustness of the watermark against different sorts of attacks, since the image regions which generate the most visible artifacts determine the final maximum strength of the watermark signal to be embedded.