1. A method for operating an image-processing device, in which an image signal on which a noise signal is superimposed is digitally transmitted between a transmitter and at least one receiver, and the image signal comprises a timed sequence of images, each containing its own image content and a noise pattern of the noise signal superimposed on the image content, wherein at least certain areas of at least two successive images of the image signal are compared to each other after the transmission, and if a difference is found between the noise patterns contained in the images, it is concluded that the images have been transmitted successfully even if the image content of the images is identical.