This is just me, but any picture I take, is open and available to anyone who wants to use them. I personally don't care (though I should, as my dad is a professional photographer), but I know there are those that do. There are ways to stamp your pictures, and there are other ways to make your pictures unavailable for copying or saving. I don't know how it's done, but there are sites out there that you can't copy or save anything.
If I do take a picture that I want or need credit for, I just come right out and say it, or put a stamp on it.