The answer is a plain and simple: no.
There isn't anything theftproof in this day and age. If a huge powerful coorporation like Warner Brothers can't keep Harry Potter movies off the internet: people like you and I aren't going to be able to control the theft of images, ideas or stories. We can only count on the intelligence and honor of the user-group we give those things to in the first place. There will always be a few idiots (maybe more than a few) who get sticky fingers: but at the end of the day -- you have the knowledge, means and creativity to create something new and they don't. If confronted by someone who knows better: they're going to flounder, get in trouble and be judged poorly... whereas you have the advantage of KNOWING beyond a doubt that your work is your own and that anyone who questions it will get a quick water-tight reply to dispell any doubt.
If you put anything on the internet... or into the public in general these days: if it's good enough to be admired -- it's good enough to be stolen. And it will be.