CAPTCHAs are tests intended to be understandable by humans but not by machines, often used to prevent computer programs from automatically registering at a website or from posting spam messages. The most common CAPTCHA is a distorted image of a word that can be easily interpreted by a human but not processed by existing computer software. For blind users, however, these reading-based CAPTCHA images are completely inaccessible. Many websites now offer audio CAPTCHAs, but these are still a problem for individuals who have multiple disabilties or cognitive difficulties in reading text.
Although considerable research has been dedicated to this field, a fully accessible CAPTCHA system has not yet been developed. Some possible alternatives include the following:
- Audio option for every visual CAPTCHA (yet this doesn’t help deaf-blind individuals).
- Other forms of authentication. For example, a user could opt to have a password sent to a personal cell phone, while the website allows a limited number of accounts per cell phone number.
- A service to exempt registered users from CAPTCHA requirements. Hypothetically, users with disabilities could register their needs, like one registers for a “disabled” license plate. These users could then be authenticated by the service to bypass CAPTCHAs or automatically be provided with an alternative of their choosing.
Discussion by Disabilities
Blind users need an alternative to image-based CAPTCHAs, such as audio options or alternative authentication methods.
Cognitive, Language, Learning Disabilities & Low Literacy
Users with cognitive, learning, and language disabilities may not be able to read the distorted word in the CAPTCHA or to understand the spoken alternative. Simpler authentication methods may be necessary.
Please note that these products are not necessarily endorsed by RtF, but represent the range of available options.
Related Research and Papers
- The Official CAPTCHA Site – Carnegie Mellon
- Inaccessibility of CAPTCHA – W3C Working Group (2005)
- Developing usable CAPTCHAs for blind users – Holman, J., Lazar, J., Feng, J. H., and D’Arcy, J. (2007)
- Achieving accessibility with self-interested designers: a strategic knowledge-acquisition approach. – da Silva, B. N., da Silva, L. H., and Garcia, A. C. (2008)
- Accessible Voice CAPTCHAs for Internet Telephony- Anu Markkola, Janne Lindqvist
- Towards a Universally Usable CAPTCHA- Graig Sauer, Harry Hochheiser, Jinjuan Feng, and Jonathan Lazar
- Accessibility of CAPTCHA methods- Sajad Shirali-Shahreza, M. Hassan Shirali-Shahreza
- An Accessible CAPTCHA System for People with Visual Disability – Generation of Human/Computer Distinguish Test with Documents on the Net- Michitomo Yamaguchi,Toru Nakata,Takeshi Okamoto,Hiroaki Kikuchi
- jCAPTCHA: Accessible Human Validation- Matthew Davidson, Karen Renaud, Shujun Li
- HuMan: an accessible, polymorphic and personalized CAPTCHA interface with preemption feature tailored for persons with visual impairments- K. S. Kuppusamy, G. Aghila
- Pedometric CAPTCHA for mobile Internet users- Sushama Kulkarni, H. S. Fadewar