Described is a technology in which a collage of digital photographs is dynamically computed and rendered so as to vary the photographs that are visible in the collage over time. A dynamic collage mechanism coupled to a source of photographs computes a collage for visible output, and dynamically updates the collage on a scheduled basis by adding different photograph(s) in place of other photograph(s). Each arrangement of the photographs in each updated collage is computed from a previous collage. Also described is layout optimization in which the photographs in the updated collage are translated, rotated and/or layered so as to cover a maximum amount of the overall area of the collage.