I have witnessed someone copy and reprint someone's skin. The maker of the skin had not liked it. I've saw people put copyrighted by :(maker of skin) on their summary, but it doesn't make much of a difference. It would be great if you could give makers the right to copyright their skins if wanted, since I know some people like to make templates.
Unfortunately this is not something that we can implement.
Or have the ability to choose wheater or not your skin can be uploaded again by anyone else before you upload it (no matter how much someone edits it after downloading it). This won't go for all skins because some people make half a skin and ask others to fix/edit it for them.