An Image-Based CAPTCHA Using Sophisticated Mental Rotation

As one of the advanced Completely Automated Public Turing tests to tell Computers and Humans Apart (CAPTCHAs), the CAPTCHA using mental rotation has been proposed. Mental rotation is an advanced human-cognitiveprocessing ability to rotate mental representations of “one” single 2D/3D object. However, as have already been reported, the mental rotation CAPTCHA can be overcome by pattern matching and/or machine learning. Therefore, this paper proposes to enhance the mental rotation CAPTCHA by using “two” distinct 3D objects in the task of mental rotation, which we call “sophisticated mental rotation”. We implemented a prototype of the sophisticated mental rotation CAPTCHA, and carried out basic experiments to confirm its usability. Also, we conducted a comparison between the proposed CAPTCHA and existing CAPTCHAs. The obtained results were satisfactory.