Like Mark said. Plus copyright belongs to the artist the moment they create something. So you are protected. Also consider Tarkhis's point. Is anyone really going to steal the average poser render and make trillions? Nope. Is someone likely to put it up on their blog or pinterest giving the the impression they did it. Yea thats possible. Though don't let that make you ruin your work by slapping large unsightly watermarks all over it or using no right-click scripts. They don't work and can actually put peoples off from looking. A small logo is enough and it can become like your brand. If you find someone directly leeching, just change the image to something rude or funny. That'll usually stop it. If it gets serious enough to take action, send a DMCA.

Pinky - you left the lens cap of your mind on again.