For those too young to remember film, or those not photographically inclined, proof sheets are the thumbnails of conventional image making. In a nutshell, a roll of film gets cut into strips, laid on top of a piece of photographic paper, a sheet of glass, turn on a light, and biff, bam, boom, you've got a quick reference print of every frame of film. Someone cut out this very tiny frame from a proof sheet. No doubt, from a commercial photo shoot.
