Proposal for CAPTCHA that Makes Use of the Human Ability to Understand Context

抄録

For the visually impaired, it is difficult to use CAPTCHA that was generated using visual information. The only way is to install a browser add-on and, by eliminating CAPTCHA, to collect information from the internet. However, it is not easy for visually impaired people to install an add-on, and there will also be disadvantages for general users if anyone is able to eliminate the CAPTCHA function. As such, using text that can be converted into voice, we proposed a sentence rearranging format of CAPTCHA that makes use of the human ability to understand context. Through experiments, we examined the kind of sentences, number of Japanese characters, number of sentences, and special characteristics of sentences that the sentence rearranging format could accommodate. Our conclusion was that, primarily, humans find it easy to understand context to the extent that the subject of the sentence is clearly indicated and is linked to the content of the sentence, that it is appropriate to use four sentences or fewer as multiple-choice options in problem sentences, and that less than 100 Japanese characters is ideal for the number of characters.