Paul Baecher, Niklas Büscher, Marc Fischlin, Benjamin Milde. Breaking reCAPTCHA: A Holistic Approach via Shape Recognition. In Jan Camenisch, Simone Fischer-Hübner, Yuko Murayama, Armand Portmann, Carlos Rieder, editors, Future Challenges in Security and Privacy for Academia and Industry - 26th IFIP TC 11 International Information Security Conference, SEC 2011, Lucerne, Switzerland, June 7-9, 2011. Proceedings. Volume 354 of IFIP Advances in Information and Communication Technology, pages 56-67, Springer, 2011. [doi]