Digital watermarking which allows tampering to be detected on a block-specific basis

Abstract

An apparatus for generating codes includes a quantization unit which generates quantization coefficients by performing discrete wavelet transform with respect to each of tiles into which an image is divided, a block division unit which divides the quantization coefficients into blocks, a Hash conversion unit which performs Hash conversion based on the quantization coefficients of each of the blocks so as to produce a Hash value for each of the blocks, a digital watermark embedding unit which adjusts a parity of a quantization coefficient of interest equal to a parity of the Hash value of a block to which the quantization coefficient of interest belongs, and a coding unit which generates code sequence data by coding the quantization coefficients including the quantization coefficient whose parity is adjusted.