The W3C Web Accessibility Initiative Protocols and Formats Working Group has published a note on the Inaccessibility of CAPTCHA: Alternatives to Visual Turing Tests on the Web. According to the note,
Web sites with resources that are attractive to aggregators (travel and event ticket sites, etc.) or other forms of automation (Web-based email, weblogs and message boards) have taken measures to ensure that they can offer their service to individual users without having their content harvested or otherwise exploited by Web robots.
The most popular solution at present is the use of graphical representations of text in registration or comment areas. The site attempts to verify that the user in question is in fact a human by requiring the user to read a distorted set of characters from a bitmapped image, then enter those characters into a form.
Researchers at Carnegie Mellon University have pioneered this method, which they have called CAPTCHA (Completely Automated Public Turing test to Tell Computers and Humans Apart) [CAPTCHA]. Various groups are at work on projects based on or similar to this original, and for the purpose of this paper, the term "CAPTCHA" is used to refer to all of these projects collectively. A Turing test [TURING], named after famed computer scientist Alan Turing, is any system of tests designed to differentiate a human from a computer.
This type of visual and textual verification comes at a huge price to users who are blind, visually impaired or dyslexic. Naturally, this image has no text equivalent accompanying it, as that would make it a giveaway to computerized systems. In many cases, these systems make it impossible for users with certain disabilities to create accounts, write comments, or make purchases on these sites, that is, CAPTCHAs fail to properly recognize users with disabilities as human.
