@ossobuco,
It certainly looks like a panel, Osso, and you're probably right in thinking that this is just a part of something bigger.
My guess, if it IS genuinely old, is that it is part of an old Spanish Church artwork, and probably painted by a local artist.
I've no idea how much it would be worth, but I'm guessing that it's not exactly an old Master. I think they call this type of work 'naive'.
Wouldn't do any harm to send a few piccies to a well respected Art Gallery or Auctioneer, just in case.