Can I use any photo paper?

Normal photo paper is often porous and can absorb the resin, making your image blotchy or discolored. Unless you'd like to do some experimenting, it's best to use the Little Windows Special Photo Paper, which is waterproof and forms a permanent bond with your printer inks, so that when you place it in your liquid resin, it won't bleed or run.

If you have any other types of paper or printed photos you'd like to use, you can add a waterproofing coating like Mod Podge to both sides and edges.  Allow to dry completely before applying resin.