Multilingual Highlighting CAPTCHA

There are many websites specially designed for mobile phones. Some hackers write automated programs to abuse these website services and waste the website resources. Therefore, it is necessary to distinguish between human users and computer programs. Methods known for achieving this are known as CAPTCHA (Completely Automated Public Turing test to tell Computers and Human Apart). CAPTCHA methods are mainly based on the weaknesses of OCR (Optical Character Recognition) systems and ask the user to type a word. So using them is difficult in tools such as PDAs (Personal Digital Assistant) or mobile phones that lack a complete keyboard. In this paper, a new CAPTCHA system is proposed for touch-screen devices such as PDAs and mobile phones. In this system, a word is drawn in a random place on the screen and a number of arcs are drawn on the screen. Then the user is asked to highlight the word by the stylus. Due to the limitations of the PDA and mobile phone, OCR programs on these devices cannot recognize the shown word, while a human user can easily highlight the word. The proposed method is implemented by the JavaME (Java Platform Micro Edition) language and tested on a Sony Ericsson P990i mobile phone.