This brings us right back to what I have been saying for some time here.....if you post anything...it will likely get stolen.  And that will continue to happen unless you make it more difficult.
Post small low res images, put on a watermark the covers the ENTIRE image...or...don't post.
I have suggested to Rendo on numerous occasions to add a "standardized" Rendo watermark on all uploads if requested by the author....but no one seems to want that.

@ Inshaala...yes, posting small is one option...but with new up-resing software out there you can upsize 4 to 6 times with very little quality loss.

I have severely cut down on my uploads here since I discovered my images had also been "borrowed".....and as I previously stated to Rendo staff I am still deciding whether or not to continue uploading here in the future.  In its current format, Renderosity is like a freebie shopping mart for image thieves.

I wish everyone success in getting their works removed from that site....but remember, there are probably several others out there that you are not aware of.....

In youth, we learn....with age, we understand.