A method and an apparatus process digital images. The method according to one embodiment accesses element data representing a plurality of elements belonging to a plurality of digital images; performs a similarity analysis between the elements from the plurality of elements to obtain inter-relational data results relating to the elements; and performs clustering of the plurality of elements, the step of performing clustering including incorporating in the inter-relational data results at least one hard constraint relating to elements from the plurality of elements, to obtain constrained inter-relational data results, performing a spectral analysis to obtain eigenvector results from the constrained inter-relational data results, and performing discretization of the eigenvector results using constrained clustering with a criterion to enforce the at least one hard constraint to obtain clusters.