somewhat OT related to file compression

Reading a response about compression made me remember a picture I once came
across on the net. I wonder if anyone knows what I'm talking about and can
provide a link to it...

Its a math trick thats related to the way files are compacted. Its a
picture of a polygon divided up into a bunch of puzzle pieces, like in the
Tetris game. The pieces each have their own colour. In a second picture
you see the same shape with the pieces arranged a different way, but a small
square piece is left out. But there's no hole in the polygon.

I remember making a physical version of the picture just to try and wrap my
head around how its possible. But I forget it now. Anyone know this?