Disclosed is a method for identifying content within a received information signal. The method comprises receiving (S6) an information signal; generating (S8) a first data set by selecting a sub-set of data (7) using filter data; and processing (S9) said information signal with reference to said first data set to determine whether said information signal comprises particular content. Advantageously, the method further comprises processing (S 12) the information signal with reference to a second data set (6) to determine whether said information signal comprises particular content. The invention allows content sharing sites such as YouTube to check whether uploaded files violate copyright rules in case the upload includes contents that was previously downloaded by the client. By keeping a list of contents that clients have downloaded, the server has an indication of a subset of contents that will likely be included in the next upload by the same client. As this subset is relatively small, a finer fingerprint resolution may be applied to this subset.