1. A digital watermark embedding device, comprising: digital-watermark-pattern generating means for generating a digital watermark pattern based on embedding information; motion-detecting means for dividing a picture signal into a plurality of blocks, the picture signal to be digitally watermarked, detecting a plurality of motion vectors representing motion detected between a given two frames of the picture signal and being associated with the plurality of blocks such that a given one of the plurality of motion vectors is associated with a particular one of the plurality of blocks, for extracting, from the plurality of blocks, respective picture regions of blocks such that the motion vectors of the blocks of a given picture region are substantially identical, the picture regions defining a plurality of objects, at least one of the plurality of objects being defined by a different sized region than that defining at least another of the plurality of objects, for performing, for each one of the plurality of objects, a predetermined evaluation of the motion vectors of the blocks of that object to generate optimal motion information defining a single motion vector for that object, for performing a further predetermined evaluation of the defined motion vectors for each one of the plurality of objects to generate optimal motion information on the entirety of the picture signal representing motion within the picture signal that is most readily detectable by the human eye, the optimal motion information defining a single further motion vector, and outputting the motion information defining the single further motion vector; modulating means for modulating the digital watermark pattern in the picture signal using only the single further motion vector so that the digital watermark pattern is moved to follow the motion represented by the single further motion vector; and embedding means for embedding the modulated digital watermark pattern within the entire frame of the picture signal.