An Accessible CAPTCHA System for People with Visual Disability - Generation of Human/Computer Distinguish Test with Documents on the Net

摘要

We propose a new scheme of CAPTCHA that does not become a perceptual barrier for disable people. Our CAPTCHA system generates the tests in verbal style, so its use is not limited in specific perceptual channels. The tests are composed of several phrases and there are two kinds of tests: Human users try to (1) distinguish a phrase of strange meaning from others, and (2) identify the common topic among them. In our test we utilize open documents for material. Note that there is quite a large amount of documents on the net, so we can generate brand-new tests every time. One may say that adversaries can look for the phrases over the Internet and get several hints. Our system hides the sources by substituting the consonants of the phrases against such an attack. The mechanism is designed to imitate the phenomenon called "consonant gradation" of natural languages.