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: for each snippet of the reference data elements that begins at successively shifted reference data element, identifying a segment associated with each snippet; and identifying one of the snippets as the best matching snippet, based on each snippet's associated segment; wherein the similarity measure for the query video stream relative to the reference video stream comprises at least one characteristic of the best matching snippet's associated segment.