I'm apparently out of the loop. What's a "spray" in relation to Steam?
If all you're talking about is some sort of picture tho, well, you're looking at MS Paint, Paint.net, or GIMP as pretty much the primary three free options. MS Paint is very limited, and lousy for much of anything other than a quick crop job or text overlay IMO. Paint.net isn't bad, although I haven't used it much (seeing as I do have and prefer Photoshop). GIMP is fairly powerful, but its interface leaves a lot to be desired, and it can be pretty complicated to figure out how to do some simple things, since it doesn't seem to like sticking to standard interface options quite to much.
"How do I get rid of a Trojan Horse?" -Sailor_Kakashi "Leave it outside the gates of Troy overnight." -Davel23