METHOD AND SYSTEM FOR WATERMARKING AN ELECTRICALLY DEPICTED IMAGE

摘要

A system for watermarking (222) an image file selects coefficients using a selection procedure that is kept secret, and assigns the selected coefficients to coefficient pairs. To detect an unauthorized alteration after the image file has been watermarked, coefficient pairs are selected using the same secret procedure that was originally used to generate the raw signature (418) values. The raw signature values may be grouped into sets, which are mapped onto shortened signature (422) codes having reduced number of bits.