Yi Xu, Gerardo Reynaga, Sonia Chiasson, Jan-Michael Frahm, Fabian Monrose, Paul C. van Oorschot. Security Analysis and Related Usability of Motion-Based CAPTCHAs: Decoding Codewords in Motion. IEEE Trans. Dependable Sec. Comput., 11(5):480-493, 2014. [doi]
Abstract is missing.