And all you need to issue a DMCA complaint is copyright. Which you automatically have upon instantiation your own original works. People in this community successfully issue DMCA complaints all the time about their images being posted on other sites. I know because they post about it in journals at dA. It's not at all uncommon, and on most sites, it doesn't seem to be difficult. Most people here would have a fit if someone took one of their renders and used it to make a new, public work without their permission. I think it's pretty fair to give photographers, character designers, and other artists the same respect we expect from others. Golden rule and all.