1. An image providing device for providing a mosaic image of an original image divided into a plurality of regions, the image providing device comprising: an image acquisition unit that acquires an image specified by a user; a candidate determination unit that, on the basis of color information of the acquired image and color information of the plurality of regions of the original image, determines a set of candidate regions among the plurality of regions to be candidates for an assignment region to which the acquired image is assigned; an edge degree acquisition unit that acquires edge degrees indicating degrees of edges in the set of candidate regions determined as the candidates; an assignment determination unit that, on the basis of the acquired edge degrees, determines the assignment region among the set of candidate regions to which the acquired image is assigned and the acquired image is preferentially placed at the assignment region; and a presentation unit that outputs a mosaic image, in which, the acquired image is placed on the basis of the assignment region determined by the assignment determination unit.