An information processing system (1) includes an operation amount data acquisition unit (109), an image data acquisition unit (101), a difference expression extraction unit (108), and a mirror surface region identification unit (111). The operation amount data acquisition unit (109) acquires operation amount data of an object. The image data acquisition unit (101) acquires image data captured by an imaging device mounted on the object. The difference expression extraction unit (108) extracts a difference expression representing feature information about a difference between two images based on two pieces of image data captured before and after the operation of the object. The mirror surface region identification unit (111) identifies a mirror surface region based on a correlation between the difference expression and the operation amount data.