1. A method for associating with a digital image a class of a plurality of classes characterized by respective models, the method comprising the following phases in sequence: dividing the digital image pixel by pixel into a respective region belonging to a set of regions comprising sky, far mountain, near mountain, and land that are predefined and different from each other on the basis of their type of content, including assigning to each pixel a data item identifying the respective region to which the pixel belongs, said identifying data item comprising a digital value, that comprises a gray level, the set of digital values assigned to the pixels of the digital image in said assignment operation corresponding to a digital gray-level image divided into regions, said division being effected by establishing whether or not a pixel of said image belongs to a respective region on the basis of an operation of analyzing the parameters that include the identifying data item of this pixel, the analysis operation carried out by verifying that said parameters satisfy pre-established conditions or logico-mathematical relationships or both that belong to the respective region and that are neither neural network nor gradient based, acquiring from the digital image divided into regions information relating to the regions to be found in it, comparing the acquired information with at least one model characterizing a respective class of said plurality of classes, associating with the digital image a class of said plurality of classes on the basis of said comparison phase, and a phase of segmenting the digital image prior to the dividing phase, the digital output image of the segmentation phase divided into one or more areas that are chromatically substantially homogeneous and comprising a reduced range of colors as compared with the input image of the segmentation phase.