Predetermined image processing is performed in accordance with an input operation performed by an input device having image pickup means for taking an image of one or a plurality of imaging targets. Target image data, which is obtained from one target image of the one imaging target or a plurality of target images of the plurality of imaging targets in the image taken by the image pickup means and which indicates a distance between the plurality of target images or a size of the one target image, is sequentially obtained. A display image is enlarged and reduced in accordance with a change in the target image data. Then, the display image processed in such a manner is displayed on a display device.