A UK team has discovered that modern high-resolution digital images are now so highly detailed, that they can enlarge the eyes in people's photos and retrieve images of out-of-shot bystanders reflected on their corneas.
Couple this with the fact human beings are quite effective at recognizing faces, even from poor quality images, and the makings of a rich forensic resource for solving crimes are only a snapshot away.
In the past it would be logical to presume that if one was wielding the camera, then they would not be featured in the picture.
However, a new study published in the journal PLOS ONE is now flipping this assumption on its head
"The pupil of the eye is like a black mirror. To enhance the image, you have to zoom in and adjust the contrast. A face image that is recovered from a reflection in the subject's eye is about 30,000 times smaller than the subject's face," said lead investigator Dr. Rob Jenkins, of the Department of Psychology at the University of York.
For the study, Jenkins and fellow researcher Christie Kerr, of the School of Psychology at the University of Glasgow, zoomed in on high-resolution passport-style photographs and retrieved images of the faces of bystanders from reflections in the eyes of the photographed subjects.
In spite of the rather low resolution of the blown up images (some of them were only 27 pixels wide), observers were able to accurately identify who the bystanders were.
When observers were presented with the images in a face-matching task, they were able to identify the tiny faces 71% of the time for unfamiliar faces and 84% of the time for familiar faces.
In a second test of unprompted recognition, the observers were able to consistently name a familiar face from just the low-resolution eye reflection image.
"Our findings thus highlight the remarkable robustness of human face recognition, as well as the untapped potential of high-resolution photography," said Jenkins.
The researchers suggest their study shows it may well be possible to use this knowledge to help solve crimes.
For instance, analyzing images reflected in the eyes of victims photographed in child sex abuse or hostage situations, or images of people recovered from cameras seized as evidence in investigations, could give way to major clues about perpetrators or their affiliates, or link individuals to particular locations.
The team hopes to apply this form of crime fighting with modern day forensics in the near future.