CAPTCHA is a security measure designed to prevent automated use of websites with distorted image of letters and numbers. CAPTCHA is an acronym for “Completely Automated Public Turing test to tell Computers and Human Apart” was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University.
For example, humans can read the distorted text which is shown below, but not a automated computer programs:
Use of CAPTCHAs, including
- Prevent Comment Spam in Blogs/ website
- Prevent Automatic Website Registration
- Prevent Email Addresses From Scrapers
- Prevent Online Polls result manipulation
- Prevent Dictionary Attacks
- Search Engine Bots
- Prevent Worms and Spam
If you run a website that suffers from problems with spam, you can put reCAPTCHA on your site. Over 100,000 sites use reCAPTCHA, including biggies Facebook, Ticketmaster, and Craigslist. You can obtain a free, secure and accessible CAPTCHA for your website, which is available from the reCAPTCHA project.