I've never really thought about doing this, but there are professional photographers out there who sell their photos for a few dollars each up to thousands of dollars for indefinite exclusivity rights for full sized 24MP photos.
See the strobist article on Yuri Arcurs here or read his own blog.
In any case, there are quite a few rules you need to follow, and the real money doesn't start pouring in until a few thousand photos have been downloaded. Photographers can get better photo prices if they only sign up with one stock site, but it'd be a while before much money started to flow.
But the thought of earning money for photos I've already taken is appealing. Perhaps thousands upon thousands of dollars by reaching out to the Internet and letting it work its sales magic. That's real magic.
