You're automatically granted a copyright the moment the work is created, but there's still a system for registering items. If you're serious about this, it's worth looking into.
I'd also advocate getting yourself hard copy proof. Even if you just did a one off digital printing run for yourself and a few other people, that should be sufficient.
What I find is the hardest part (as a photographer) is actually finding the people committing the violation. It's easy if they take your work and turn it into a blockbuster movie or change a few words and end up on Oprah's book club, but if you're rather small time about it and so are they, there in lies the rub.
Lastly, nothing you can do will prevent people from being able to copy it. Even if you create a print version rather than an online version, it can be OCR scanned and turned into a document. This happens every day. You've got to do what you can to protect yourself and then just put it out there. Sharing your work is better than keeping it locked up because you're afraid someone is going to make it their own.