An Efficient Ellipse-Shaped Blobs Detection Algorithm for Breaking Facebook CAPTCHA

Abstract

A CAPTCHA is a test designed to distinguish computer programs from human beings, in order to prevent the abuse of network resources. And nowadays, academic researches on CAPTCHA, including designing friendly but secure CAPTCHA systems and breaking existing CAPTCHA systems, are becoming a more and more hot topic. Breaking an existing CAPTCHA system can help to perfect its designs and therefore to improve its security. In this paper, ESBDA, an Ellipse-Shaped Blobs Detection Algorithm, is proposed to detect the ellipse-shaped blobs used in Facebook CAPTCHA scheme, which can be used to break the Facebook CAPTCHA system. The approach is based on detecting the contour of the ellipse-shaped blobs on the basis of erosion and dilation technologies. And the experimental results show that ESBDA can effectively remove the noised ellipse-shaped blobs in the Facebook CPATCHA scheme. © Springer-Verlag Berlin Heidelberg 2013.