A method of signing prediction-coded video data comprises: obtaining a coded
video sequence comprising a set of frames including at least one
intra frame having independently decodable image data, and at least one
inter frame, containing image data decodable by reference to another frame; generating a group hash of the coded
video sequence by hashing the image data of the coded
video sequence; generating a plurality of individual hashes of frame subsets including at least one frame by hashing the image data derived from each of the frame subsets, reducing the length of each of the individual hashes to a length shorter than a total length of the group hash, generating a
digital signature by encrypting at least the group hash and the individual hashes with reduced lengths; providing the group hash and the reduced length individual hashes together with the
digital signature and the coded video sequence.