A video signal is coded by generating, at a transmitter, a difference signal (at 2) representing the differences between a picture to be transmitted and a predicted picture based on a stored locally decoded picture. This is decoded to generate a fresh locally decoded picture. The transmitter also generates a check signal, such as a CRC, as a function of the locally decoded picture. The receiver decodes the difference signal to create a decoded picture. It compares the decoded picture with the check signal, and generates an error signal if the two do not tally.