An image processing system includes an illumination unit and an illumination control unit configured to adjust light emitted from the illumination unit so as to illuminate a limited area in a space, the system generates a timing signal for controlling emission/non-emission of light from the illumination unit, captures a first image of an imaging area including the limited area or part of the limited area based on the timing signal, the first image being taken from a position different from the illumination unit when the illumination unit emits light, captures a second image of the imaging area based on the timing signal, the second image being taken from the position when the illumination unit emits no light, and acquires a third image which is a difference image between the first image and the second image.