3. The method of claim 1 , wherein said step of building a database of reference files comprises collecting files previously ranked according to the predefined scheme, under a digital format; obtaining feature vectors of each of the collected files; and storing the feature vectors in a database of reference files.
4. The method of claim 3 , wherein said step of building a database of reference files further comprises storing a rank, defined according to the predefined scheme, of each of the reference files in a score database.