Patent ID: 6983058

Claim:
A method of embedding watermark information in master data, said method comprising the steps of: (a) causing the master data to be subjected to discrete Fourier transform; (b) adding a minute variation, which corresponds to a phase difference pattern determined in advance as the watermark information, to either one of a real number array and an imaginary number array of the master data obtained by the discrete Fourier transform, so as to generate resulting data with the minute variation added thereto; (c) causing the resulting data with the minute variation added thereto to be subjected to inverse Fourier transform, so as to generate authorized data with the watermark information embedded therein; (a0) causing the master data to be subjected to a predetermined data transform, which converts the master data to a specific data form that enables an area mainly corresponding to a low frequency component to be specified prior to the discrete Fourier transform in said step (a); and (ax) carrying out an inverse transform of the predetermined data transform performed in said step (a0), after the inverse Fourier transform in said step (c), wherein said step (a) causes a specific data portion, which represents the area mainly corresponding to the low frequency component and is selected out of the data converted in said step (a0), to be subjected to the discrete Fourier transform.