With the widespread of computing and mobile devices, authentication using biometrics has received greater attention. Although biometric systems usually provide good solutions, the recognition performance tends to be affected over time due to changing conditions and aging of biometric data, which results in intra-class variability. Adaptive biometric systems, which adapt the biometric reference over time, have been proposed to deal with such intra-class variability. This article provides the most up-to-date and complete discussion on adaptive biometrics systems we are aware of, including formalization, terminology, sources or variations that motivates the use of adaptation, adaptation strategies, evaluation methodology, and open challenges. This field of research is sometimes referred to as template update.

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