Four experiments investigated matching of unfamiliar target faces taken from high-quality video against arrays of photographs. In Experiment 1, targets were present in 50% of arrays. Accuracy was poor and worsened when viewpoint and expression differed between target and array faces. In Experiment 2, targets were present in every array, but performance remained highly error prone. In Experiment 3, short video clips of the targets were shown and replayed as often as necessary, but performance levels were only slightly better than Experiment 2. Experiment 4 showed that matching was dominated by external face features. The results urge caution in the use of video images to identify people who have committed crimes. Superficial impressions of resemblance or dissimilarity between face images can be highly misleading.The human face provides the most reliable means of person identification available to the human eye (although fingerprints and iris patterns may prove more useful for automated identification; e.g., seeDaugman, 1998). Nonethe-

People can be inaccurate at matching unfamiliar faces shown in high-quality video images, even when viewpoint and facial expressions are closely matched. However, identification of highly familiar faces appears good, even when video quality is poor. Experiment 1 reported a direct comparison between familiar and unfamiliar faces. Participants who were personally familiar with target items appearing on video were highly accurate at a verification task. Unfamiliar participants doing the same task performed very inaccurately. Familiarity affected discriminability, but not bias. Experiments 2 and 3 showed that brief periods of familiarization have little beneficial effect unless "deep" or "social" processing is encouraged. The results show that video evidence can be used effectively as a probe to identity when the faces shown are highly familiar to observers, but caution should be used where images of unfamiliar people are being compared.

Recent research has shown that unfamiliar face matching from both high-and low-quality closed circuit television video images to photographs is highly prone to error, even when viewpoint and expression are matched as closely as possible. The current experiments made use of a ®lmed, staged reconstruction of a bank raid that was captured on CCTV and on high-quality broadcasting video. Experiment 1 tested the ability of members of the public to match actors captured on CCTV to photo-spreads containing similar-looking distractors. Further experiments, each testing different groups of subjects, investigated matching ability using both high-quality photographs (Experiment 2) and broadcast-quality video material (Experiment 3). Experiment 3 also investigated the effect of disguising hairstyle, and varied whether or not the target was present in the photo line-up. The results of these experiments con®rm those of previous work, that matching the identity of unfamiliar faces is highly fallible, even when high-quality footage is used. Experiments 4 and 5 tested matching ability using two-alternative forced-choice and single-item veri®cation tasks. Performance remained highly error-prone even with the simplest question asked. The legal implications of the results are discussed.

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Human subjects perform poorly at matching different images of unfamiliar faces. When images are taken by different capture devices (cameras), matching is difficult for human perceivers and also for automatic systems. We test an automatic face recognition system based on principal components analysis (PCA) and compare its performance with that of human subjects tested on the same set of images. A number of variants of the PCA system are compared, using different matching metrics and different numbers of components. PCA performance critically depends on the choice of distance metric, with a Mahalanobis metric consistently outperforming a Euclidean metric. Under optimal conditions, the automatic PCA system exceeds human performance on the same images. We hypothesise that unfamiliar face recognition may be mediated by processes corresponding to rather simple functions of the inputs.

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