ek22 wrote:
But then I take that image, open it as a new layer on my own xcf and voila, comments enabled. The thing with thievery is, the more clever you get trying to avoid being stolen from, the more clever they get trying to steal your stuff. Not saying that this is a good thing, it's just what popped into my head when I saw your comment. If I thought of it I'm sure some nefarious derptart(<---that's not the word I had in mind btw.) probably did too.
Unless you have a big fat visible watermark in the middle of your image, you cannot prevent anyone from "borrowing" it. If you want to prove later that you are the author, your best bet is to keep a more detailed version of the very same image (ie, downscale or crop before publishing). Keeping up your sleeve the original XCF, or, for photography, the "raw" file or other images from the same shooting session may also help.