Visual word-based CAPTCHA using 3D characters

A secure login authentication for Web applications is presented. The proposed technique uses a CAPTCHA to discriminate between users and automated programs designed to access Web applications. The novelty of the proposed CAPTCHA resides on the use of 3D characters with 3D boundaries delimited by shadows. The robustness of the proposed CAPTCHA is increased by applying random distortions in each character according to geometric transformation in a 3D space. In particular, shadows obtained from different light effects are used to further enhance security against automatic character recognition tools. Experimental evaluations are reported to confirm the security of the approach.