1. An image processing device, comprising at least one microprocessor configured to: acquire a photographed image of a real-world space from a photographing device that photographs the real-world space; cause a virtual space image representing a situation of a virtual space as viewed from a given viewpoint to be displayed on a display; set a target region in the photographed image; dispose a background object representing a background, which is photographed outside the target region of the photographed image, in the virtual space; dispose a subject object representing a subject, which is photographed inside the target region of the photographed image, in the virtual space, and dispose the subject object between the given viewpoint and the background object so that a position at which the subject object is displayed and superimposed on the background object in the virtual space image, and a position of the target region in the photographed image, correspond to each other; and dispose a composition target object, which represents a composition target displayed and combined with the real-world space in the virtual space image, between the background object and the subject object, wherein the at least one microprocessor, in the virtual space image, display the composition target object superimposed on the background object, and display the subject object superimposed on the composition target object.