1. An image processing device comprising: an image processing unit configured to generate an output image using a first image obtained by imaging a real space from a first viewpoint as an input image, wherein, based on a position and a posture of the first viewpoint in the real space, the image processing unit generates, as the output image, a second image obtained by virtually imaging the real space from a second viewpoint having a position and a posture different from the position and the posture of the first viewpoint in the real space, wherein the first image is displayed together with the second image based on a relation between the position and the posture of the first viewpoint, wherein the image processing unit sets a restriction on a change amount of the position and the posture of the second viewpoint, based on a change of the position and the posture of the first viewpoint, wherein, when the display of the first image is deviated by a predetermined proportion or more from a range of the second image, the image processing unit releases the restriction, and wherein the image processing unit is implemented via at least one processor.