METHOD FOR FINDING IMAGES IN JPEG FORMAT WHICH CONTAIN A DIGITAL WATERMARK

FIELD: steganography, in particular, methods for detecting additional information in graphic images in JPEG format, having various degrees of significance in form of a digital watermark. ^ SUBSTANCE: invention allows detection of digital watermark size and coordinates of modified discontinuous cosine transformation coefficients of JPEG format file with required error probability. Along perimeter of each image block, correlation coefficient relative to adjacent blocks are determined for all image blocks, analyzed block after forced modification - incrementing by one in accordance to complete enumeration method of one or several absolute values of discontinuous cosine transformation coefficients (not equal to 0 and 1) - and reverse discontinuous cosine transformation is restored in spatial area. Along perimeter of restored block, values of coefficients of correlation with adjacent blocks are calculated. Minimum of distance is determined - minimum of average square deviation between values of correlation coefficients of restored image block, restored fragment from a corresponding set of discontinuous cosine transformation coefficients is the most correlated with adjacent fragments, and its restored discontinuous cosine transformation coefficients characterize the digital watermark. ^ EFFECT: increased efficiency. ^ 3 dwg