Via Boing Boing, shake your head slightly—as if signalling no (or affirmation in some parts of Greece and the Balkans) to reveal a hidden image in the seemingly uniform bars plus a brilliant tutorial on how to make one’s own with any image. Perhaps a clever engineer could using this method—which is a variation on the Bezold effect in gradated contrast, slip in a secret subliminal message into one of the sections of picket fence steel slats of Trump’s Border Wall.