This is some pretty slick software, called Shape Collage, available for Mac/PC/Linux and it’s FREE!
I pointed the application to a few hundred iPhone photos (most of them from SXSW) on my computer (it can also traverse web url’s for photos or even my local Aperture library), then hand drew a cactus shape and it then arranged all the photos in the shape I drew:
You should view this larger to see the detail. There is (of course) a group on Flickr for these as well.
Pretty amazing and cool with endless possibilities.
(found via CyberNet)