Implementation of CAPTCHA suitable for mobile devices

Abstract

CAPTCHA is a technology designed to prevent automated programs (known as bots) from acquiring access to on-line accounts to send spam mail, manipulate vote numbers in on-line polls, or take other malicious actions. In addition, access to Web services has been incorporated into mobile devices, such as smartphones. However, because most CAPTCHAs are not designed for mobile devices, user-friendly CAPTCHA for mobile devices is required. Thus, we implemented CAPTCHA on mobile devices and evaluated its resistance to bots. Our CAPTCHA showed robustness against bots, with good usability.