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 according to a mode of coding determined for said zone, wherein said prediction step comprises, in relation to said current partition: partitioning anew at least one portion of the reference causal zone into a plurality of reference partitions; determining motion vectors respectively associated with reference partitions obtained subsequent to the new partitioning; determining a predictor motion vector based on said determined motion vectors; and predicting the motion vector of said current partition based on said determined predictor motion vector.