Bitmap editing

I have a 2D game I'm making which will require a lot of overlayed sprites and bitmaps, and in an effort to elliminate any possibility of over-working even the slowest computer I've been looking for a way to overlay each sprite that I'd be adding onto one large background bmap, so that the game only has to be constantly opening that one image instead of several different ones. Is there a way to do that? The only ways I've found have been by taking a screenshot and saving it into a bmap and loading that, which I can't do because I'll have other panels and objects floating around in front of the background image that can't remain stationary. Any suggestions?

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