1. A collage image creating method which creates a collage image by arranging a plurality of images comprising: a first step that creates a collage image by determining arrangements of the plurality of images according to a placement algorithm using a weighted distance function that is based in part on an aspect ratio of each image as a parameter, the placement algorithm is a centroidal voronoi tessellation that uses the weighted distance function; and a second step that recreates a collage image by re-executing the first step according to at least one of a change due to an addition or deletion of an image which configures the collage image, a change in arrangement position of at least one image among images which are included in the collage image, a change in rotation angle of at least one image among images which are included in the collage image, and a change in arrangement size of at least one image among images which are included in the collage image.