A real camera image of a real space that is captured by a real camera is obtained. Color information about a plurality of sampling points in the real camera image is obtained. Next, an average color is calculated based on the obtained color information about the plurality of sampling points. Based on the calculated average color, parameters relating to the color and brightness of a light source set in a virtual space are set. A virtual object image is generated by capturing, with a virtual camera, an image of a virtual object existing in the virtual space, which virtual object is illuminated by the light source whose parameters have been set. Then, a superimposed image, in which the virtual object image is superimposed on the real camera image, is generated and displayed on a display device.