As a member of the W3C‘s Cognitive and Learning Disabilities Accessibility Task Force, I agreed to review web-security technologies. I chose to begin with CAPTCHA. My first draft is below. The format I am using is the one I intend to use for future reviews. All the text is my own.
I welcome your feedback, additions, and/or revisions.
CAPTCHA is typically a website widget that prevents automated programs from submitting a web form intended for humans by requiring humans to pass a test. Such tests present distorted text visually and/or aurally; and require the form-submitter to enter that text into a field, and invoke a submit button. See http://www.captcha.net/
Problem
CAPTCHA often blocks people with physical and/or cognitive disabilities who cannot discern the text they are required to enter and submit. The scope of the problem is vast because, for example, people with disabilities are prevented from purchasing goods and registering for services on the (probably) millions of websites that use CAPTCHA.
People with Cognitive Disabilities May Not Be Able to:
- read CAPTCHA text at all because of the intentional distortion of it
- comprehend text that can’t be enlarged without additional distortion
- have the advantage of comprehending the meaning of words or images
- understand text spoken in a computerized and distorted voice
- complete the multi-step procedure for submitting the CAPTCHA text
- complete a timed CAPTCHA due to slowness in completing all steps
- understand the purpose of buttons such as reset, listen, and help
- recognize functional elements, such as buttons, are clickable
- focus due to irrelevant instructions such as “stop spam” and “read books”
- become accustomed to CAPTCHA because there are multiple versions of it
Alternatives
- Inaccessibility of CAPTCHA: Alternatives to Visual Turing Tests on the Web, World Wide Web Consortium, November, 2005.
- A Sliding Alternative to CAPTCHA?, L. Wroblewski, June, 2010.
- sweetCaptcha: Fun and Human Friendly Captcha
Notes
- Neil Milliken suggested I add that people may not be able to complete CAPTCHAs correctly due to sequencing problems causing them to input the characters in incorrect order. I will do so in my next draft.
- No endorsement of CAPTCHA or its alternatives is intended or implied.