Serendipity35

You probably have come across a CAPTCHA online lately. It's a challenge-response test that is used by many sites to try to insure that the person posting a message or registering is a human and not some spambot. We use a simple one on this blog when you post a comment, and it works pretty well at preventing bots, but allows annoying humans to post garbage that we still have to clean out.

The most common ones ask you to copy a few characters from a distorted image.

The contrived acronym CAPTCHA was created (and trademarked) at Carnegie Mellon University to mean "Completely Automated Public Turing test to tell Computers and Humans Apart." (It might also be described as a reverse Turing test.)

For whatever good it does online, it is really bad for accessibility. The entire idea makes it difficult or impossible for people who are visually impaired, blind, or dyslexic to use them. It's one thing to stop a commenter, but there's also the blocked registration or online order. Accessibility is still an area that doesn't get enough attention by designers (web or otherwise) and social networking sites are full of roadblocks.

The American Foundation for the Blind posted an article about some of the problems. The video embedded below is a demonstration of some of those problems.

The video gives you a sense of what it is like to use a social site with a screen reader.

There are some alternatives to allow users to prove they are human (logical puzzles and audio, the latter also not free of accessibility problems). There is more information on the W3C site.