In fingerprint-based biometric authentication, the threshold on the matching score required to accept a user as genuine is made stricter (higher). Which change generally occurs?

Answer: C. The false acceptance rate (FAR) falls and the false rejection rate (FRR) rises

Biometric authentication expresses how well the captured features match the enrolled features as a score and accepts the user as genuine if the score is at or above a threshold. The false acceptance rate (FAR) is the rate at which impostors are wrongly accepted, and the false rejection rate (FRR) is the rate at which genuine users are wrongly rejected. Making the threshold stricter makes it harder for impostors to pass, so FAR falls, but genuine users whose score is lower than usual, because of finger placement or dry skin for example, are rejected more often, so FRR rises. FAR and FRR thus trade off: moving the threshold lowers one and raises the other. The threshold is set to keep FAR low in security-critical uses and FRR low where convenience matters. The value at which FAR and FRR are equal (the equal error rate, EER) is used as a guide for comparing systems.

• A. Moving the threshold alone cannot lower both at once. Lowering both requires improving the sensor or the matching method itself.
• B. This is what happens when the threshold is relaxed.
• C. Correct. A stricter threshold makes it harder for impostors to pass, but genuine users are also rejected more often.