FACE RECOGNITION AS A FUNCTION OF DISTANCE AND ILLUMINATION - A PRACTICAL TOOL FOR USE IN THE COURTROOM

This paper describes a practical courtroom tool that provides insight in face recognition accuracy as a function of distance and illuminatio n. Subjects were shown 3/4 target portraits with an exposition time of 12 seconds, immediately followed by a target-absent or target-present lineup of six full-face portraits. Subjects were asked to identify th e target. Seven distances (3 to 40 meter) and nine illumination levels (0.3 to 3000 lux) were used which resulted in a 79 matrix, with in t he cells a hit score and a false alarm score. From these rough data se veral other measures were derived, like d-prime, diagnostic value and some idealised scores. The scores represent the upper margins of recog nition accuracy with the memory component reduced to a minimum. The re sults clearly indicate a systematic increase of recognition performanc e with decreasing distance and increasing illumination. The end result is a practical rule of thumb, the Rule of fifteen: Even in ideal cond itions the desired diagnostic value of 15 is reached at not more than 15 meters, not less than 15 lux.