User blog comment:Abgar/Petit Forest- pixel artist minigame/@comment-9531161-20140309034300/@comment-9531161-20140309054426

Hmm, if you make the easel take up only one layer and make sure nothing is in the other layer, you could store the picture number for the easel there. For instance, you could have three designated spots on the GRP for three different pictures. You could keep a small section of 3 pixels for "used" or "unused". When the player places an easel, it looks through the used and unused section to see which GRP spot it can take up. If they're all full, the user can't place the easel. It'll save the GRP spot (0, 1, or 2) in the unused BG layer save portion. When the player paints on the easel, it'll look at this index to figure out which GRP spot to use. When you destroy the easel, you just uncheck the "used" pixel for that picture.

I guess that is a little complicated though lol. If you're not willing to put up with all that, then a single image is still great.