1. A method of coding a digital image, comprising: subdividing at least a portion of the image into image blocks formed by a plurality of pixels; and processing each image block, wherein said processing comprises, for a generic current image block being processed: determining a skip-mode prediction block with respect to the current image block being processed, calculating a difference between the image block being processed and the skip-mode prediction block, comparing the calculated difference to a predetermined threshold; and determining, for the current image block being processed, prediction image blocks, electing one among the determined prediction image blocks and coding a difference between the elected prediction image block and the current image block, wherein at least one among said determining, electing, and coding is performed conditioned to a first result of said comparing the calculated difference to the first threshold, wherein said calculating a difference between the current image block being processed and the skip-mode prediction block comprises: calculating a plurality of pixel-by-pixel differences, wherein each of said pixel-by-pixel differences is calculated between a pixel of the current image block and a corresponding pixel of the skip-mode prediction image block; associating a respective quantized value with each of said pixel-by-pixel differences; and performing a combination of the quantized values so as to obtain a cumulated value representing said difference between the current image block being processed and the skip-mode prediction block, wherein said associating a respective quantized value is performed such that a contribution of a first group of pixel-by-pixel differences to a second cumulated value, obtainable by performing said combination on the values of said pixel-by-pixel differences, is higher than a contribution of a corresponding first group of quantized values to said cumulated value, wherein said pixel-by-pixel differences of the first group have an absolute value lower than a second threshold.