Assessment of Time Dependency in Face Recognition: An Initial Study

As face recognition research matures and products are deployed, the performance of such syslemsis being scrutinized by many constituencies. Performance factors of strong practical interest include the elapsed time betwccn a subject's enrollment and subsequent acquisition of an unidentified face image, and the number of images of each subject available. In this paper, a long-term image acquisition project currently underway is described and data from the pilot study is examined. Experimental results suggest that (a) recognition perJormance is substantiaUy poorer when unknown images are acquired on a different day from the enrolled images, (b) degradation in performance does not follow a simple predictable pattern with time between known and unknown image acquisition, and (c) performance figures quoted in the literature based on known and unknown image sets acquired on the same day may have little practical value.