LOL Mod Podge is good stuff, eh? I would think if you got under the picture with a knife, it should come off from the metal. You might have to use a blade and cut all around it, but it should come off!

Mod podge is mostly white glue with a little bit of water based urethane. Put a damp sponge on top of the pic and let it sit a bit first. This could cloud the pic if you want to save it tho.
kathy

Thank you for your input. I went to the MP site and turns out they have a MP called MP Hard. Sounds like what I'm needing so I ordered it and the outside MP...