Verifying that a live human is interacting with an automated speech based system is needed in some applications such as biometric authentication. In this paper, we present a method to verify that the user is human. Simply stated, our method asks the user to repeat a sentence. The reply is analyzed to verify that it is the requested sentence and said by a human, not a speech synthesis system. Our method is taking advantage of both speech synthesizer and speech recognizer limitations to detect computer programs, which is new, and potentially more accessible, way to develop CAPTCHA systems. Using an acoustic model trained on voices of over 1000 users, our system can verify the user's answer with 98% accuracy and with 80% success in distinguishing humans from computers.
Bibliographic reference. Shirali-Shahreza, Sajad / Ganjali, Yashar / Balakrishnan, Ravin (2011): "Verifying human users in speech-based interactions", In INTERSPEECH-2011, 1585-1588.