Computer Science Research on Alternatives to Visual-Based

¶ … Computer Science

Research on Alternatives to Visual-Based CAPTCHAs for Sight-Impaired Users

Created to block the Web bots used by spammers, CAPTCHA ("Completely Automated Public Turing Test to Tell Computers and Humans Apart") is a technology used to verify that a person, rather than an automated system, is entering the data. A visual-based CAPTCHA shows distorted text and then users type in what they see in order to proceed. Users encounter CAPTCHAs in a variety of different Internet activities, such as submitting online comments and forms, creating email accounts, and registering for networking sites [1].

Because CAPTCHAs cannot be read by machines, the screen-reading software used by blind computer users cannot read the text either [2], which leaves these people unable to use the Web sites. This paper reviews the literature on CAPTCHA alternatives for blind and sight-impaired users.

Proposed Alternatives to Visual-Based CAPTCHAs

Audio-based CAPTCHAs

In Developing Usable CAPTCHAs for Blind Users, the authors propose that instead of text, CAPTCHAs use a combination of images and sounds. This CAPTCHA displays an image of an object along with the sound it makes, allowing users to indentify it using either their eyesight or hearing [3]. The researchers tested on five blind users and five sighted users, and all five of the blind users made at least one error but were eventually able to enter in the correct terms [3]. The methodology is clearly presented, but a small test group is a limitation of the study.

In Spoken Captcha: A Captcha System for Blind Users, the authors propose using a sound clip, with the user responding with the matching word [4]. A speech file of the user's voice is created, and the system then checks to ensure the word matches and to verify that the voice is not synthesized. Testing, which involved 256 users, found 92.5% accuracy with this method [4]. The researchers tested a large user group and present detailed test results, but a limitation is that only English words and English speakers were used in the research.

2. Computational CAPTCHAs

In Pitfalls in CAPTCHA Design and Implementation, the authors reviewed the use of math CAPTCHAs, where users solve math problems to proceed [5]. The program was designed for technical users of the Center for Informatics and Computing of the Ru-er Boskovic Institute, and the math problems, such as derivates and polynomials, are challenging [5]. This approach is likely too difficult for many users, so the implementation of this method and the use of this study's results are limited.

In CAPTCHA for Blind People, the authors propose using simple math problems that are then converted to speech; when the sound is played, the user enters the answer [6]. The proposed system is thoroughly described, but a limitation of the paper is that it involves no testing; the authors only present their theories.