1. A non-transitory recording medium storing a program that causes a computer to execute a process, the process comprising: generating a modified image by executing modification processing on an image indicating a predetermined mark affixed to a product body, wherein a feature amount of the modified image differs from a feature amount of the image of the predetermined mark or another modified image by more than a specified reference amount; providing the generated modified image as a determination-use image to determine whether a product affixed with the predetermined mark is included in a captured image; and detecting the product affixed with the mark from the captured image using the determination-use image.