Method of embedding digital watermark, storage medium in which the method is stored, method of identifying embedded digital watermark, and apparatus for embedding digital watermark

摘要

The procedure of the present invention specifies predetermined elements included in a matrix F which is obtained by Fourier transform of master image data P 0 (step S 122 ), and adds a minute variation DeltaF of a predetermined magnitude to either a real number array FR or an imaginary number array FI of the predetermined elements (step S 124 and S 126 ). Here note that the minute variation DeltaF should be subtracted from corresponding elements, in order to keep the symmetry of the Fourier spectrum. A resulting image obtained by an inverse transform of the matrix with the minute variation DeltaF added thereto includes a phase difference pattern W 01 that is embedded therein and corresponds to the minute variation DeltaF. As long as a master image is closed to the public, this embedded pattern can not be taken out of the resulting image nor be deleted by overwriting attacks. Even if the processed data with the digital watermark embedded therein is exposed to overwriting attacks of different pieces of watermark information by the similar algorithm, the arrangement of the information enables the digital watermark embedded in the master data to be taken out accurately. The similar series of processing may be carried out with regard to a specific area of the low frequency component obtained by wavelet transform of the mater image.