To be honest, I think the best defense (even more so than watermarks and all that) is being an active part of a network like Dribbble, Behance, or even here. I've gotten tips from people I've spoken to maybe once before on work that was being shared without attribution, all because I was visible and active on those networks. So, while it may be tempting to shell up and watermark the ever-living out of your work, keep creating, keep posting it, and the general community will (usually) keep an eye out for your work. Think about it -- there are guys who post work all the time, and you know their styles. I hate to use the ever-common example of Fraser, but his work is unique and he spreads it far and wide. When someone steals his work, everyone knows because they've seen it somewhere. The more often you create those exposure opportunities, the more likely you'll be alerted by a fellow community member (if you don't catch it yourself). If I see something familiar, I always look around to see if it's something I recognize for a reason, and then let the artist know. Yu Masuda's Bengal actually made it on to one of MVPTees' shirts, so I sent him a quick note. We're much stronger as a community, think of it that way. It sucks that it happens, but threads like this give me a little bit of hope that our work is somewhat protected still.