K. Chan, I. King, und M. Yuen. Proceedings of the International Conference on Computational Science and Engineering, CSE '09, 4, Seite 1205--1210. (August 2009)
M. Ageev, Q. Guo, D. Lagun, und E. Agichtein. Proceedings of the 34th international ACM SIGIR conference on Research and development in Information Retrieval, Seite 345--354. New York, NY, USA, ACM, (2011)
L. von Ahn, und L. Dabbish. CHI '04: Proceedings of the SIGCHI conference on Human factors in computing systems, Seite 319--326. New York, NY, USA, ACM, (2004)
R. Jesus, D. Goncalves, A. Abrantes, und N. Correia. Computer Vision and Pattern Recognition Workshops, 2008. CVPR Workshops 2008. IEEE Computer Society Conference on(Juni 2008)