This paper summarizes a study carried out on data from the Face Recognition Vendor Test 2006 (FRVT 2006). The finding of greatest practical importance is the discovery of a strong connection between a relatively simple measure of image quality and performance of state-of-the-art vendor algorithms in FRVT 2006. The image quality measure quantifies edge density and likely relates to focus. This effect is part of a larger four-way interaction observed between edge density, face size and whether images are acquired indoors our outdoors. This finding illustrates the broader potential for statistical modeling of empirical data to play an important role in finding and codifying biometric quality measures.