In an electronic watermark embedding technique, even when image data compression such as MPEG2 compression is conducted for image data of an image including a watermark while keeping deterioration of picture quality within an allowed range, the electronic watermark is kept retained. A watermark embedding operation and an MPEG2 encoding operation as well as a watermark detecting operation are cooperatively executed. Specifically, in the WM embedding operation, information regarding an operation state of an MPEG2 encoder, particularly, information regarding an amount of data is received. According to the received information of data, parameters such as the total amount of the watermark to be embedded, strength thereof, and an embedding position thereof are controlled.