A method is provided for checking an image inspection system having a camera system with a camera, an illumination apparatus for targeted illumination of a printing substrate, an image processing computer, and a main computer, for quality control of products of a printing substrate processing machine by using the main computer. A reference image is entered and transmitted to the main computer, a current printing image recorded by the camera system is transmitted to the image processing computer, a partial image in a suitable region of the current printing image, not being printed with printing image data, is selected in the image processing computer, the partial image is analyzed by comparison with the reference image in the image processing computer, and the inspection system is assessed based on the analysis of the partial image by the main computer and any defects of the inspection system being found are indicated.