Superimpositions.

Elegant, subtle images result from the automated combination of 50 photographs bearing the same Flickr tag. (Via Metafilter.) Here, for example, is what 50 superimposed photographs tagged "The Gates" look like. Here's "Eiffel." A Metafilter commenter notes the similarity of the effect to this set of images that uses mean averaging to produce a single image combining every Playboy centerfold from an entire decade.