US Patent 7154560 Watermarking of digital image data

Digital watermarks can serve to indicate copyright ownership of digitized video. When video images are transmitted as transformed by discrete cosine transformation (DCT) for compression, with or without motion compensation, it is advantageous to include a watermark after transformation. To this end, a DCT watermark is generated for optimal visibility based on the original image data, and the generated watermark is superposed on the transformed data.