I have used CAPTCHA on my various web sites in the standard manner where I generated some obfuscated string of characters (odd pair of words, random number, etc.) in an image for the user to manually reproduce in a text box. I am also aware of recaptcha.net which extends the basic functionality of screening bots from humans and as well as helping to digitize books. I just came across another way of performing CAPTCHA with the AJAX Fancy CAPTCHA jQuery plugin which rather than asking the user to reproduce a string instead asks the user to drag an image that is readily recognizable (scissors, pencil, book, etc.) into an area that is equally recognizable. When I saw this I had to say to myself "WOW...that's cool!"
Question: Does anyone out there have any other examples of a neat and different way of performing CAPTCHA without having to generate a random string of characters into an image for the user to try and read (or regenerate until they can) so that they can manually type it into a box?
I'd like to see ReCAPTCHA implemented for images that a computer can't tell whether or not they're pornography. Web filter companies could pay free porn sites to use this system to better fill out their blacklists. The free porn sites could then make more porn, and the web filters would have more porn to block.