Fingerprinting segments of data content for version identification

A method of detecting a version of input data content in which the data content is arranged as two or more segments according to a segmentation pattern; and versions of the data content are identifiable by corresponding identification data patterns by which at least some of the segments have respective identification data; comprises the steps of detecting identification data in respect of each segment of the input data content; comparing the detected identification data with identification data patterns corresponding to different versions of the data content; and detecting that the input data content comprises at least a contribution from a certain version of the data content if a sum of matches obtained between the detected identification data and the identification data pattern for that version exceeds a threshold number.