In the Dock: Chimeric Image Composites Reduce Identification Accuracy

Abstract

The aim of presenting chimeric images (formed from opposing halves of a pair of same or different faces) in court settings is to optimise the accuracy of identification decisions based on CCTV evidence. The experiments reported here examined the utility of this technique. Experiment 1 examined the accuracy of face matching with vertically split, aligned chimeric images, misaligned hemi-faces and full-face images. Experiment 2 replicated the first experiment but replaced the misaligned images with opposing hemi-faces separated by a gap. The final experiment used horizontally split faces. All three experiments showed that matching was less accurate with aligned chimeric images than with full-face images. Furthermore, the pattern of responses obtained with chimeric images differed significantly from full-face matching and misaligned/separated hemi-face matching. Chimeric images produced a bias towards same responses even when the face halves were different. The results suggest caution in the use of chimeric images in court.

Expert facial comparison evidence: Science versus pseudo science

“…More importantly an interaction is found such that the inaccurate responding is greatest when the face pairs are different. The increased probability that images of two different people will be judged as showing the same person is generally consistent with the findings of Strathie (2010) and Strathie et al (2012).…”

“…In general, the results showed the same pattern of responding to that found in Strathie et al (2012), with performance best for full-faces (in all presentations), coupled with an increased likelihood to judge that two different faces were the same in normal and disguised presentations (this bias was not present for different faces when degraded, but importantly the technique produced no advantage in matching accuracy).…”

“…A theoretical explanation of these findings offered by Strathie et al (2012) appeals to a broad consensus that faces are generally processed at a holistic rather than feature level (Hole, 1994;Rossion, 2009;Tanaka & Farah, 1993;Young et al, 1987). They argue that that the fully aligned composite images (whether still or moving) evoke holistic processing, thus creating a perception of a whole face, whereas the misaligned half-faces or half-faces with a gap evoke a feature based comparison.…”

Facial Wipes don't Wash: Facial Image Comparison by Video Superimposition Reduces the Accuracy of Face Matching Decisions

“…Importantly, the pattern of responding obtained in the current experiment, with video wipes, is similar to that found with chimeric images (Strathie et al, 2012), suggesting that both techniques evoke a similar processing strategy and that this impedes, rather than optimises, face matching decisions.…”

“…As the display slowly wipes back and forth between the two images, at each intermediary stage only one face appears on screen, made up of each of the two facial images in varying proportions. As each of the intermediary stages consists of a chimeric image created by a combination of the two photos, it is predicted that exposure to these composite faces will influence face matching decisions in a similar manner to static chimeric images (Strathie et al, 2012).…”