摘要：The test that is generated and graded by computers in order to check the users to be human is Completely Automated Public Turing Test to Tell Computers and Humans Apart (CAPTCHA). CAPTCHA can protect online and free services from bots that can access to services in a huge numbers. Currently, there are several different types of CAPTCHA that have been proposed. However, most of proposed CAPTCHAs have Decaptchas that can read and recognize them. However, the main problem is not security of the current CAPTCHAs that is usability of it. The way of choosing features of a Captcha that previous researchers have used was not based on the fact of Human and Computer Interaction rules. This research will propose a sort of usability features based on what users choose and what needs to be considered of Human and Computer Interaction rules in order to develop a usable CAPTCHA.
