1. A controller for controlling displaying on a display means of received video or image data which has been encoded with invisible digital watermarks integrated within the received video or image data and representing a content classification for the video or image data, the controller having connections for connecting to a display means and for connecting to a data receiver or data reading apparatus, the controller comprising: means for detecting digital watermarks integrated within the received video or image data, said received video or image data representing content for display, means for decoding the digital watermarks to obtain content classification information, and means for controlling the displaying of said video or image data in response to the content classification information obtained from the watermarks.