A watermark information embedding method, and apparatus, capable of suppressing the quality degradation of contents and increasing the survivability of embedded information. When embedding watermark information in moving picture data formed of a plurality of still picture frames arranged in time series, a motion vector representing a property specific to moving picture is detected (22, 224) for each of image blocks generated by dividing a target frame. According to a motion quantity, a pixel change factor specifying rule (32, 320) is selected (23) for each block. Out of pixels permitted to be changed in luminance depending upon the state of an image in each block representing a property specific to still picture, as many pixels as a number specified by the selected rule (33) are selected (24). Luminance change processing for forming watermark information is conducted (25) on the selected pixels.