reCAPTCHA
I recently added a contact page to my site. To do this I used a wordpress plug in, Dagon Design. Its a very good plug in by the way. It allows you to prevent spam by adding a reCAPTCHA image to the form. I’ve always known about reCAPTCHA helping to digitise books where OCR is not working, but I have always wondered how the system knows you are correct, if the word cannot be read by computers.
After I signed up for my free account at recaptcha.net I read about how it works.
Each new word that cannot be read correctly by OCR is given to a user in conjunction with another word for which the answer is already known. The user is then asked to read both words. If they solve the one for which the answer is known, the system assumes their answer is correct for the new one. The system then gives the new image to a number of other people to determine, with higher confidence, whether the original answer was correct.
You can read more about it here.
Tags: reCAPTCHA