1. A method for decoding a data stream representative of an image or of a sequence of images, said stream comprising data representative of at least one portion of one of said images, said method implementing a step of predicting a motion vector of a partition of a current image portion, with respect to a reference causal zone which has been partitioned previously into a plurality of reference partitions according to a mode of coding determined for said zone, wherein at the time of the prediction of said motion vector of said current partition, the method comprises: repartitioning the reference causal zone into a plurality of new reference partitions; calculating new motion vectors for selected ones of the new reference partitions; calculating a predictor motion vector based on said calculated new motion vectors; and predicting the motion vector of said current partition based on said calculated predictor motion vector.