1. A method comprising: defining a virtual space including a display object and a three-dimensional object; defining a first pair of virtual cameras in the virtual space including a first right-eye virtual camera and a first left-eye virtual camera; defining a second pair of virtual cameras in the virtual space including a second right-eye virtual camera and a second left-eye virtual camera; generating a first right-eye image based on the first right-eye virtual camera, and a first left-eye image based on the first left-eye virtual camera, wherein both the first right-eye image and the first left-eye image include a first part of the virtual space and the display object; generating a second right-eye image based on the second right-eye virtual camera, and a second left-eye image based on the second left-eye virtual camera, wherein both the second right-eye image and the second left-eye image include a second part of the virtual space and the three-dimensional object; superimposing the first right-eye image and the second right-eye image to overlap the three-dimensional object with the display object to form a superimposed right-eye image; outputting the superimposed right-eye image to a right-eye display unit of a head mounted display; superimposing the first left-eye image and the second left-eye image to overlap the three-dimensional object with the display object to form a superimposed left-eye image; and outputting the superimposed left-eye image to a left-eye display unit of a head mounted display.