Image inspection method with local image rectification

A method of image inspection on printed products in a machine for processing printing materials, the method comprising:

• recording and digitizing a printed product by at least one image sensor in a course of an image inspection process carried out by an image recording system to form a recorded digital printed image;
• comparing the recorded digital printed image with a digital reference image by a computer and checking with the computer for image areas with distorted regions in the recorded digital printed image;
• calculating with the computer suitable rectification factors for the image areas with distorted regions;
• rectifying the digital reference image using the calculated suitable rectification factors for the distorted image areas to generate a modified reference image;
• identifying with the computer image areas in the digital reference image that do not have enough edges for calculating suitable rectification factors, inserting anchors into the image areas, printing the anchors on the printed products and recording and digitizing with the at least one image sensor, the anchors becoming part of the recorded digital printed image, and calculating with the computer the local rectification factors with reference to the anchors;
• comparing the modified reference image by the computer with digital printed images recorded during a continuing production run;
• and
• when deviations are found in the recorded digital printed images from the modified reference image, removing printed products that have been found to be defective.