Difficult imaging covariates or difficult subjects? - An empirical investigation

The performance of face recognition algorithms is affected both by external factors and internal subject characteristics [I]. Reliably identifying these factors and understanding their behavior on performance can potentially serve two important goals to predict the performance of the algorithms at novel deployment sites and to design appropriate acquisition environments at prospective sites to optimize performance. There have been a few recent efforts in this direction that focus on identifying factors that affect face recognition performance but there has been no extensive study regarding the consistency of the effects various factors have on algorithms when other covariates vary. To give an example, a smiling target image has been reported to be better than a neutral expression image, but is this true across all possible illumination conditions, head poses, gender, etc.? In this paper, we perform rigorous experiments to provide answers to such questions. Our investigation indicates that controlled lighting and smiling expression are the most favorable conditions that consistently give superior performance even when other factors are allowed to vary. We also observe that internal subject characterization using biometric menagerie-based classification shows very weak consistency when external conditions are allowed to vary.