Fig. 2From: Presentation attack detection and biometric recognition in a challenge-response formalismDepicts a challenge-response protocol in the form of an interaction between a student Stu and a biometrician Bob. The claim is made in step 1, a challenge is issued in 2 and responded to in 3. Then, in 4, the authenticity of the initial claim has been verified, and Stu is thus a verified biometricianBack to article page