Video data is distributed as base data to represent a source image stream and enhancement data to improve the base data . The base data and the enhancement data are distributed each in the same format, so that each can be used separately to generate an image, except that the base data is encrypted and the enhancement data is not encrypted. A receiver is able to switch between a normal mode, in which the base data and the enhancement data are combined and a teasing mode, wherein an image derived from the enhancement data only is shown if no key is available to decrypt the base data.