1. An image composition device comprising: an obtaining section configured to obtain a downward-taken background image and a foreground image to be composed with the downward-taken background image; a specification section configured to specify a position at which the foreground image is composed, in the background image obtained by the obtaining section; a composition section configured to compose the foreground image at the position in the background image which is specified by the specification section, to generate a composed image; and an image processing section configured to execute a smoothing process with a process intensity controlled based on the position, on the composed image.