Captcha those spammers
Last year, we were trying to find a way to stop people from sending spam through our website. At the time we had no idea that we were actually implementing a “captcha”.
“Captcha” - Completely Automated Public Test to tell Computers and Humans Apart.
This is often implemented by rendering a word in an irregular, distorted way against a distracting background and asking the user to type it in. Failure to type in the correct word means that the form submission is rejected. It’s very, very difficult to automate that word recognition so we’re safe for a while. (Unless some spammer happens to advance the field of character recognition.)
Lots of websites do this especially ones that involve posting messages or signing up for email. The first site I noticed doing this was the Yahoo email service.
Here are some interesting references:
- I learned of the term “Captcha” from Vincent Massol’s blog.
- He rightly points out that this is a good solution to the problem of blog comment spam.
- Vincent Massol’s colleagues are developing a Java-based toolkit to vend captchas, called JCaptcha. See http://jcaptcha.sourceforge.net/
- The computer science behind this is discussed in: L. van Ahn, M. Blum and J. Langford, Telling Humans Apart Automatically, Communications of the ACM, 47(2), February 2004.