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 pixel blocks of the image being processed and/or temporal motion vectors associated with determined pixel blocks of an already processed image; generating candidate motion vectors from the selected motion vectors; calculating an error for each of the candidate motion vectors; determining a penalty for at least one subset of the candidate motion vectors; electing a motion vector from among the candidate motion vectors based on the error that is calculated and the penalty that is determined; and storing information associating the elected motion vector with the current pixel block, wherein in the determining step, the penalty is determined according to values of the pixels of that pixel block in the preceding original image from which the candidate motion vector points to the current block and/or according to values of the pixels of that pixel block in the following original image to which the candidate motion vector points from the current block.