Achint Thomas, Kunal Punera, Lyndon Kennedy, Belle L. Tseng, Yi Chang. Framework for evaluation of text captchas. In Leslie Carr, Alberto H. F. Laender, Bernadette Farias Lóscio, Irwin King, Marcus Fontoura, Denny Vrandecic, Lora Aroyo, José Palazzo M. de Oliveira, Fernanda Lima, Erik Wilde, editors, 22nd International World Wide Web Conference, WWW '13, Rio de Janeiro, Brazil, May 13-17, 2013, Companion Volume. pages 159-160, International World Wide Web Conferences Steering Committee / ACM, 2013. [doi]
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