1. A motion estimation method for processing images intended to be inserted, between a preceding original image and a following original image, into a sequence of images, each of the images being divided into a plurality of pixel blocks, and a motion vector being associated with each of the pixel blocks of a processed image, the method comprising, for a current block of an image being processed, the steps of: selecting spatial motion vectors associated with respective pixel blocks of the image being processed and temporal motion vectors associated with respective pixel blocks of a preceding processed image; generating candidate motion vectors from the selected motion vectors; electing a motion vector from among the candidate motion vectors; and storing information associating the elected motion vector with the current pixel block, wherein a temporal motion vector is selected only if it satisfies a determined selection criterion based on the orientation of the motion vector.