A Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) is designed to distinguish humans from machines. Most of the existing tests require reading distorted text embedded in a background image. However, many existing CAPTCHAs are either too difficult for humans due to excessive distortions or are trivial for automated algorithms to solve. These CAPTCHAs also suff...

Text CAPTCHA has been an effective means to protect online systems from spams and abuses caused by automatic scripts which pretend to be human beings. However, nearly all the Text CAPTCHA designs in nowadays are based on English characters, which may not be the most userfriendly option for non-English speakers. Therefore, under the background of globalization, there is an increasing interest in...

Password alone is currently not trusted for user online authentication and security as threats from hackers continue to grow, requiring highly efficient defense safeguard protection against unauthorized users. Therefore, CAPTCHA techniques came into the picture an automated assistance distinguish between humans robots. The has several applications in domain be merged with encrypted hash functio...

CAPTCHA (or Human Interaction Proof) is now almost a standard security technique for defending against undesirable or malicious bot programs on the Internet. However, the robustness of CAPTCHAs has so far been studied mainly just in communities such as computer vision, and document analysis and recognition. This paper motivates a security engineering perspective of the robustness of CAPTCHAs. S...

Due to the significant increase in threats, attacks and vulnerabilities that affect the Web in recent years has resulted the development and implementation of tools and methods to ensure security measures in the privacy, confidentiality and data integrity of users and businesses. Under certain circumstances, despite the implementation of these tools do not always get the flow of information whi...

Based on the notion of “emergence”, Xu et al. (Usenix Security 2012; TDSC 2013) developed the first concrete instantiation of emerging-image moving-object (EIMO) CAPTCHAs using 2D hollow objects (codewords), shown to be usable and believed to be secure. In this paper, we highlight the hidden security weaknesses of such a 2D EIMO CAPTCHA design. A key vulnerability is that the camera projection ...