1. A method of sorting postal articles into a postal sorting frame comprising sorting slots, in which method said articles to be sorted are placed in a stack, and the articles are taken one-by-one from the top of the stack so as to place each of them in a sorting slot, and digital images of the top of the stack are formed automatically at a certain rate, said method being characterized in that it further comprises the following steps: a) recording said digital images in the memory of a data-processing unit; b) mutually comparing said digital images on the basis of a certain graphical resemblance criterion, so as to form image models, each of which is representative of one or more successive digital images that are similar-looking; c) associating each image model with data indicating a persistence time; and d) applying a time filter to said image models so as to eliminate those models whose persistence time is less than a certain threshold value, the remaining image models serving as a basis for automatically counting the sorted postal articles that are sorted in the slots of the frame.