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 of the image signal to the at least one receiver, and when a difference is found between the noise patterns contained in the certain areas of the at least two successive images, it is concluded that the at least two consecutive images have been transmitted successfully even when the image content of the certain areas of the at least two successive images is identical.