Personally, I assume that publishing on the web implies the possiblity that someone "rips off" your images. However, as Michael points out, at web resolutions, they are definitly not going to make 40x50 fine art prints!
I personally add my name to each photograph that I publish. I started this approach last year. Certainly, people can clone over my photograph to erase my name. But, such people will not be bothered by any form of copyright protection whatsoever, so, as I said, you have to accept this as a risk of publishing on the web.
People can also scan and reprint photographs published in books & magazines. There's no absolute protection when it comes to publishing.