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