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 acquisition unit that acquires an image specified by a user; a first search unit that searches for a region satisfying conditions where the acquired image can be assigned; a first assignment unit that assigns the acquired image to the region searched for by the first search unit; a dividing unit that further divides any one of regions to which no image is assigned into a plurality of regions when there is no region satisfying the conditions where the acquired image can be assigned as a result of the search by the first search unit; a second assignment unit that assigns the acquired image to a region satisfying the conditions where the acquired image can be assigned among the plurality of regions formed by the division by the dividing unit; and a presentation unit that, on the basis of the assignment by the first assignment unit or the second assignment unit, causes a mosaic image in which the acquired image is placed to be presented.