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: analyzing a digital image pixel by pixel to determine parameters of each pixel by verifying that each parameter satisfies at least one of pre-established conditions, logico-mathematical relationships, or both pre-established conditions and logico-mathematical relationships that are associated with respective predefined regions comprising sky, land, and mountain, and 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 based on the analysis, 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, a 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, 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.