I just came across [url=http://recaptcha.net/]reCAPTCHA[/url], a cool little script that allows us to kill two birds with one stone: protect web pages from spam and further the digitization of books.
CAPTCHAs are “reverse Turing tests” which are designed to prove an actual human is interfacing with a website. Ever since about 2003, spam bots have made open message boards and guestbooks a pretty much untenable feature for websites… they are quickly filled up with all sorts of spam links for v1@gra and the like.
CAPTCHAs create a distorted text challenge image which is relatively easy for humans to read, but almost impossible for the bots to decipher. If the text is correctly deciphered, the comment is permitted; if not, it’s blocked. Thereby greatly reducing comment spam by automated means. Boo-ya, bots!!
reCAPTCHA takes this one step further, by providing challenge images based on words that OCR scanners (which are busy digitizing the world’s books for us to enjoy) were not able to decipher. So the estimated 10 seconds it takes you to decipher the CAPTCHA challenge image serves the dual purpose of clarifying a word a computer couldn’t sort out. Like I said, two birds, one stone.
They’ve also got a cool email protector which I’ve employed on this website. This allows me to avoid having yet another stream of junk email, by both hiding my real address via their system, and eliminating a form on my website for the spambots to fill with spam. Yay!