Something you didn’t know about CAPTCHA


Captcha Example

You know those annoying boxes that make you enter a few words into a box before you can continue submitting a comment/downloading a file/some other action, they’re called CAPTCHA or Completely Automated Public Turing tests to tell Computers and Humans Apart. Their main purpose is to help in preventing spam, but there’s another bonus reason behind them that you probably didn’t know about.

By entering the words in the box, you are also helping to digitise texts that were written before the computer age. The words that you see are taken directly from old texts that are being scanned and stored in digital format in order to preserve them and make them more accessible to the world. Since some of the words in these texts are difficult for computers to process, it uses the results of human efforts to help decipher them. That’s why the sign says ‘stop spam, read books’.

Now I’m sure a lot of you are probably wondering how the test verifies the answer as correct if it doesn’t know the correct answer itself. Here’s how: Each new word 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.

So despite being annoying as hell sometimes and I’d say that there are better methods of spam prevention out there, using CAPTCHA isn’t a complete waste of your precious time after all.