After more than a century of biometric usage for forensics and physical identification, and decades of evolution of biometric technology at a measured pace, we are now in the middle of a biometric revolution, fueled by the availability of biometric sensors in smartphones, tablets, and laptops and, more recently, by breakthroughs in biometric technology. The usage of biometrics is becoming routine in everyday life, as fingerprints are used for unlocking smartphones, selfies are used for online identity proofing, and banks use speaker verification for customer authentication; and machines are now claimed to be better than humans at identifying faces (Lu and Tang 2015).