1. An image forming apparatus comprising: a shape information acquisition unit configured to acquire shape information indicating a shape of a three-dimensional object on which an image forming process is to be performed; a surface determination unit configured to determine a plurality of surfaces from which the three-dimensional object is constructed, based on the shape information; and an output image information generation unit configured to generate surface image information and join region image information, the surface image information being information on images to be formed on the respective surfaces, each image being of a region obtained by cutting an end of the corresponding surface by a predetermined amount, the join region image information being information on an image to be formed on a join region between the adjacent surfaces.