1. A method of watermarking a video signal by applying a watermarking function to motion vectors calculated by estimation of movement between images of the video signal, the method comprising the following steps: applying the watermarking function to at least some of the calculated motion vectors; and generating the watermarked video signal by compensating movement with the aid of the watermarked motion vectors, the watermarking function being applied with the aid of a binary marking key, each bit of which is associated with at least one selected motion vector, wherein, in order to apply the watermarking function, the method further comprises the following steps: marking the coordinates of the selected motion vector ({right arrow over (V)})in a reference space divided into a plurality of predetermined portions; defining two complementary zones Z 0 and Z 1 in each portion, one of the two zones being situated inside the other one; assigning a binary value to each of the two zones; and where necessary, modifying the coordinates of the selected motion vector so that it is in the zone of the portion to which it belongs, of binary value which corresponds to the bit of the marking key with which the selected motion vector is associated.