Hacking Chinese touclick CAPTCHA by multi-scale corner structure model with fast pattern matching

Conference Name:2014 ACM Conference on Multimedia, MM 2014. Conference Address: Orlando, FL, United states. Time:November 3, 2014 - November 7, 2014.ACM SIGMM; et al.; FXPAL; Google; IBM; SymantecIn this paper, we tackle the challenge of hacking CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart), which is widely used to identify machine and human in web page registration and authorization [17]. More specially, we target at touclick Chinese CAPTCHA that is recently popular in mobile application scenario. Hacking such CAPTCHA is much more challenging and left unexploited in the literature. Our main idea is a multi-scale Corner based Structure Model, termed CSM, with a very efficient pattern matching scheme. CSM can accurately capture the intrinsic statistics of touclick Chinese CAPTCHA against background clutters. We demonstrate the efficiency and effectiveness of the proposed approach by extensive experiments on a Chinese touclick CAPTCHA dataset collected from Internet forums. We report encouraging results with an overall success rate of almost 100% and an averaged detection speed of 170 millisecond. Upon our work, we also provide suggestions on improving the current CAPTCHA-based human-machine identification systems