when i was in college, i studied art + art history
and wrote a 30 page paper piet mondrain.
somehow, while doing the research i came upon the work
of laszlo maholy-nagy, i found one of the photograms that pretty much changed the way i thought about photography.
http://www.geh.org/fm/amico99/htmlsrc2/m198121630071_ful.html#topofimage
until then, a photograph had to be of something that was recorded with a camera, and a photogram was just something you did in your first photo-class when you emptied your pockets ( pebbles, lint, paperclips, pennies, good luck charms, frogs and everything else ) ... and got the outline of it all.
the way mahloy-nagy used photo paper, objects and light to paint a 3-d image pretty much changed everything.
(if you every want to see his "light prop" and the film he made from it "black white and gray" go to the fogg museum at harvard university. they have one of the 3 props, and the film that (at least they used to ) plug-in and show on a weekly basis. well worth it if you are into 30s abstract imagery.)