just found a few very interesting stamps. These stamps are made of plastic, with some kind of "3D"-effect. You can't see the effect in the photos, though.
These are referred to as "Lenticular" stamps,
I have one on piece, however the "stamp" will/would not accept
ink of course, from the canceller so it looks dodgy.
The ultimate "reusable stamp"
Try Googling "lenticular"