Cut up some metal, printed out a picture, glued it on. Put it on a ring base. Boom, nyan cat ring.
The "ring base" is actually a buckle from a purse that connected the bag-part to the strap. It fit around my finger and it had a flat top, so hey, why not?
I'd cover it with something, too. Plastic? Clear nail polish? Varnish? Hey, you could use Saran wrap and I'm sure it'd work just fine. xD Have fun!