Visual Cryptography

The exceptionally cool follow-on to this is David Chaum's work on using visual cryptography for voting --

  http://www.constitution2.org/wiki/files/2004_chaum_secret_ballot_receipts.pdf

People have since built further on that work, but I seem to recall that Chaum's paper is what started a wave of work on end-to-end verifiable voting.

Awesome! I (almost) didn't believe the fish thing. I had to PRT-SCR and use paint.net to change the white to transparent to overlay them. It's real!