1. A method to detect video copying, comprising: providing a set of reference data elements derived from a set of reference video frames in a reference video stream; providing a set of query data elements derived from a set of query video frames in a query video stream, each of the query data elements having a corresponding query data element identifier; associating with each of the reference data elements a fingerprint selected from among the query data element identifiers; and determining a similarity measure for the query video stream relative to the reference video stream by a comparison of the query data element identifiers to the fingerprints.