GENERATING FINGERPRINTS OF VIDEO SIGNALS

The present invention provides novel techniques for generating more robust fingerprints (1) of video signals (2). Certain embodiments of the invention derive video fingerprints only from blocks (21) in a central portion (22) of each frame (20), ignoring a remaining outer portion (23), the resultant fingerprints (1) being more robust with respect to transformations comprising cropping or shifts. Other embodiments divide each frame (or a central portion of it) into non-rectangular blocks, such as pie-shaped or annular blocks, and generate fingerprints from these blocks. The shape of the blocks can be selected to provide robustness against particular transformations. Pie blocks provide robustness to scaling, and annular blocks provide robustness to rotations, for example. Other embodiments use blocks of different sizes, so that different portions of the frame may be given different weighting in the fingerprint.