glue or gel medium
800 grade sandpaper
varnish or sealant
This is worked on one of the white plastic dominoes. Next set I buy I think I will look for a set of wooden ones, they will be much easier to attach fittings too. The white plastic type are quite difficult to drill through, and they let off a horrible stink, which leads me to think that the fine white dust can't be terribly good for you.
Prepare your domino by first drilling a hole at the top for the hanger, and at the bottom for the bling.
Lightly sand the domino to give the glue and paint a tooth to adhere too. Using gel medium, or your glue of choice, attach an image to both front and back of the domino. Let dry thoroughly and sand the edges of the image to ensure a flush fit. Use a skewer to poke through where you drilled the holes.
Paint the edges with acrylic paint, and when dry finish with a coat of varnish, or sealant, whichever you prefer. Attach a hanger and some bling.