You may want to research NET PAINT which is free and will let you put your work on LAYERS. Then you can hide or delete a layer when you need it gone.
Ok, so.. Recently I've been using MS Paint for some projects; design, and computer art. I've gotten permission from my teacher, so I can trace photos on Paint, then fill them in later and make them my own. But as I did this, I could not figure out a way to remove the picture, while still keeping my 'traced' work. I swear I've seen someone doing this before, but I cannot figure out how. If anyone has some suggestions, I wold be grateful.