That's the risk you run when you offer free stuff. There's no escaping it, so if it bothers you, stop offering them. Sounds harsh, but it's something I live by. I offer free 2D stuff, as well as original and unique Photoshop tutorials, on my blog, and not only do I see people using the stuff without crediting me, I see them use my bandwidth on top of that by not saving the freebie to their own server, and I see them create their own tutorials, using my techniques (which I know were unique to me because I discovered them through play and then searched all over for anything similar before posting them) and not even mentioning where they learned the technique from. Even then it never bothers me because the freebies and tutorials I share are only a tiny part of what I do, just the barest hint of my true techniques, the leftovers, the stuff I don't mind sharing because I have even better stuff that I keep to myself ... if that makes any sense. (Plus, I genuinely enjoy sharing my more basic stuff and having people learn or benefit from them.) So, my advice? Don't give away anything that you'd hate to see others claiming as theirs. It's not worth the pain you go through when the worst kind of people abuse your generosity.