Face recognition processes
in the context of line-ups

In police line-ups, the identification of faces can be the decisive factor in solving a crime. For practical and financial reasons, face-to-face line-ups are now rarely carried out, but instead the method of so-called photo-line-ups is used. Due to current data protection regulations, distractor images of real people are often not presented in these photo-line-ups, but faces are recreated using photo editing programs. This is often done by “mixing” images of real people with each other so that a new face is created from the images (so-called morphing). So far, however, there have only been a few studies on the extent to which morphed images may be perceived differently from non-morphed images.

An initial study was able to show that morphed images are at least perceived as more attractive than non-morphed images (Langlois & Roggman, 1990). A higher attractiveness could lead to a more positive attribution of the depicted person in the sense of the so-called halo effect (Dion et al., 1972) and thus to an influence on the identification performance: Accused images could be less positively attributed and more frequently selected as perpetrator:in. One study shows that attractiveness actually influences the selection in the photo line-up (Grüner et al., 2021). However, the influence of morphing on the fairness of photo line-ups has not yet been investigated.

As part of the project, we conduct two experiments that address the question of whether morphing has an influence on the witnesses' identification decision. We use two types of manipulation: on the one hand, we create morphed images by mixing two images of two real (and similar to the accused image) persons. On the other hand, we present caricatured distractor images. Morphed faces often have “prototypical” facial features, as morphing averages the distinctive facial features of individual faces with the facial features of other people, making them less distinctive. In caricatures, on the other hand, the distinctive facial features of individual people are emphasized. Such caricatures are perceived as less attractive than original images (Valentine et al., 2004). In terms of perceived attractiveness, caricatures could therefore represent a counterpoint and possibly an alternative to morphed images in police practice, as they would create a bias “away from the perpetrator”. If, under real circumstances, a picture of the accused is selected in such a “caricature line-up” despite this bias, the decision could be regarded as significantly more valid (the selection was then not made on the basis of attractiveness/sympathy, but should be based on an actual identification performance).