Abstract: A device for controlling the transport of a printing product by a print-related machine includes at least one locally stationary photoelectric detector having a light transmitter, by which light is directed at a surface of the printing product, and at least one light receiver for detecting the light remitted from the surface, a device for evaluating the remitted light, the evaluating device having computational equipment connected to adjustment elements for controlling the effect of a cyclically operating transporting device, the light transmitter including a light source for transmitting coherent light, and the light receiver including an element for recording the spatial distribution of the stray light, a timing device provided for synchronizing the instant of time of the recording with the cycle of the transporting device, and the evaluation device having a comparator for the local distribution of the stray light at the instant of time of the recording provided with a prescribed distribution.