Protein domain classification is a useful tool to deduce functional properties of proteins. Many software to classify domains according to available databases have been proposed so far. This paper introduces the notion of "fingerprint" as an easy and readable digest of the similarities between a protein fragment and an entire set of sequences. This concept offers us a rationale for building an automatic SCOP classifier which assigns a query sequence to the most likely family. Fingerprint-based analysis has been implemented in a software tool and we report some experimental validations for it.