1. An image composition apparatus configured to produce a composite image in which a foreground image is overlaid on a part of a background image, the apparatus comprising: an image designation unit configured to designate a pair of images used as the background image and the foreground image; an information obtaining unit configured to, when one image of the pair of images is a pictorial image with a certain pictorial style, obtain pictorial style information indicative of the pictorial style of the one image of the pair of images; an image conversion unit configured to convert the other image of the pair of images into a pictorial image with the pictorial style indicated by the pictorial style information obtained by the information obtaining unit; a composition unit configured to produce a composite image from a combination of the pictorial image corresponding to the one image of the pair of images and the pictorial image resulting from the conversion by the image conversion unit of the other image of the pair of images; and an output unit configured to output the composite image produced by the composition unit.