1. A non-transitory computer-readable storage medium storing program instructions computer-executable to perform: analyzing image content within each image of a set of images to determine at least one respective characteristic metric for each image; determining a respective transition effect for each pair of a plurality of pairs of the images based on the at least one respective characteristic metric for each image, wherein the respective transition effect is useable to implement a transition between the pair of images, and wherein said determining the respective transition effect comprises determining a region in each image of the pair to which the respective transition effect will be applied; and storing an indication of the determined transition effects.