Digital information embedding/extracting apparatus and method, and medium including a program for executing the method recorded thereon

摘要

In an embedding apparatus, an orthogonal transform section 11 divides an original image 1 into a plurality of blocks to perform orthogonal transform every block. An information embedding section 13 embeds a pseudo-random number sequence mapped with inherent digital information in part of a transform coefficients sequence obtained by the orthogonal transform using a weight sequence. In an extracting apparatus, a correlation value calculation section 23 reads sequences of transform coefficients for respective blocks from the data including the pseudo-random number sequence embedded therein in a predetermined order, and calculates an inner product between the sequences of transform coefficients and a pseudo-random number sequence. A pseudo-random number determination section 24 determines that the pseudo-random number sequence has been embedded when the inner product is greater than a predetermine threshold value. An information generation section 25 extracts inherent digital information mapped with the determined pseudo-random number sequence. This method discourages deciphering of the digital information by a third party, suppresses deterioration in image quality by a simple apparatus/method, and improves the rate of detection of watermark data.