@Webmaster4o I am not following you... once it is an image, you could erase in PIL, or by drawing the background color over top.
It comes down to whether you are trying to simulate a "paint" program, (thnk photoshop "paintbrush tool") or a vector program, like illustrator (or photoshop path tool). if the goal is to have a vector program, you don't "draw" them, you would add control points. If the goal is a paint tool, you might want to store the last few operation to facilitate undo, but at some point you end up with pixels on the screen, not paths with 1000s of points.