Iranian Society of Cryptology The ISC International Journal of Information Security 2008-2045 1 2 2009 07 25 Image flip CAPTCHA 105 123 39170 10.22042/isecure.2015.1.2.4 EN M. Tariq Banday N. A. Shah Journal Article 2009 03 19 The massive and automated access to Web resources through robots has made it essential for Web service providers to make some conclusion about whether the "user" is a human or a robot. A Human Interaction Proof (HIP) like Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) offers a way to make such a distinction. CAPTCHA is a reverse Turing test used by Web service providers to secure human interaction assumed services from Web bots. Several Web services that include and are not limited to free e-mail accounts, online polls, chat rooms, search engines, blogs, password systems, etc. use CAPTCHA as a defensive mechanism against automated Web bots. In this paper, we present a new clickable image-based CAPTCHA technique. The technique presents user with a CAPTCHA image composed of several sub-images. Properties of the proposed technique offer all of the benefits of image-based CAPTCHAs; grant improved security than that of usual OCR-based techniques, consume less Web page area than most of image-based techniques and at the same time improve the user-friendliness of the Web page. https://www.isecure-journal.com/article_39170_325f53e3727938dc321cafd8b8ce8dcb.pdf