If you've ever tried to post a comment through Blogger's software you've probably seen the little box where you have to type some random letters to ensure your post goes through. I've wanted to put that on my new blogs as well as on my sites at work since we get a ton of spam through our forms. To curtail this spam check out this
spam blocker. If you're coding the HTML form all you have to do is generate some random character in the server side language of your choice and bam, it creates the image. All you have to do is duplicate whatever you send it in a hidden "check" field. It doesn't simply send back the letters you send it for easy scraping but gives explicit instructions on how you can easily parse out its results. It's awesome.