1. A non-transitory computer-readable storage medium having stored therein an image display program which is configured to stereoscopically display a real world image onto which a 3-dimensional virtual object is superimposed on a screen of a stereoscopic display apparatus configured to provide a stereoscopic view to a user, the stereoscopic display apparatus including a computing system that includes at least one processor circuit coupled to a memory device, the memory device configured to store real world image data output by a left camera and a right camera, the image display program comprising instructions that are, when executed by a computing system, configured to: recognize a predetermined shooting target from the stored real world image data output by the left camera and the right camera; calculate multiple first position orientation information, which are each based on separate relate world image data acquired over a period of time, indicating relative positions and relative orientations of the right camera and the predetermined shooting target with respect to each other; calculate multiple second position orientation information, which are each based on separate relate world image data acquired over the period of time, indicating relative positions and relative orientations of the left camera and the predetermined shooting target with respect to each other; determine how much the calculated multiple first position orientation information and the calculated multiple second position orientation information vary; as a result of determination that the calculated multiple first position orientation information and the calculated multiple second position orientation information vary less than the predetermined amount, calculate pose data, which is indicative of a single position and a single orientation in a virtual space, as a function of multiple calculated first position orientation information and multiple calculated second position orientation information; calculate a midpoint, as the single position, between the relative position of the right camera and the relative position of the left camera; calculate a position and an orientation of a right virtual camera for generating a right virtual space image of the virtual space based on the calculated pose data; calculate a position and an orientation of a left virtual camera for generating a left virtual space image in the virtual space based on the calculated pose data; generate the right virtual space image as viewed from the right virtual camera in accordance with the calculated position and the calculated orientation of the right virtual camera; generate the left virtual space image as viewed from the left virtual camera in accordance with the calculated position and the calculated orientation of the left virtual camera; superimpose the right virtual space image onto the real world image data outputted from the right camera; superimpose the left virtual space image onto the real world image data outputted from the left camera; and output the superimposed images to the stereoscopic display apparatus for a stereoscopic view, wherein the positions of the right virtual camera and the left virtual camera are symmetrically set about the calculated midpoint.