What is an example of biometric authentication?

Biometric authentication utilizes unique physical or behavioral characteristics of individuals to verify their identity. Fingerprint or facial recognition verification perfectly exemplifies this concept, as it involves scanning and analyzing specific attributes of a person's biometric data. These characteristics are inherently unique to each individual, making them highly effective for authentication purposes.

In contrast, two-factor authentication through email relies on knowledge-based factors such as access to an email account, which does not involve any biometric data. Password strength checking is focused on assessing the complexity of a password rather than authenticating a user based on physical traits. Lastly, security questions for account recovery are also knowledge-based and do not incorporate biometric elements. Thus, the chosen answer is the only one that aligns with the definition of biometric authentication.