The eyes are not just the mirror of the soul, they also mirror the world around us. Now, a UK team has found that today's high-resolution digital images are now so detailed, they can enlarge the eyes in people's photos and retrieve images of out-of-shot bystanders reflected on their corneas.
Combine this with the fact human beings are very efficient at recognizing faces, even from poor quality images, and you have the makings of a rich forensic resource for solving crimes.
In the past it would be reasonable to assume if you were the one wielding the camera, then you would not be in the picture.
But a new study published in the journal PLOS ONE is now turning this assumption on its head.
Lead investigator Dr. Rob Jenkins, of the Department of Psychology at the University of York, says:
"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."
For the study, he and co-researcher Christie Kerr, of the School of Psychology at the University of Glasgow, zoomed in on high-resolution passport-style photographs and recovered images of the faces of bystanders from reflections in the eyes of the photographed subjects.
Despite 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 another test of spontaneous recognition, the observers were able to reliably name a familiar face from just the low-resolution eye reflection image.
Dr. Jenkins says:
"Our findings thus highlight the remarkable robustness of human face recognition, as well as the untapped potential of high-resolution photography."
The researchers suggest their study shows it may well be possible to use this knowledge to help solve crimes.
For example, analyzing images reflected in the eyes of victims photographed in child sex abuse or hostage situations, or images of people retrieved from cameras seized as evidence in investigations, could yield vital clues about perpetrators or their associates, or link individuals to particular locations.
Meanwhile, a study published in the Proceedings of the National Academy of Sciences in 2010 found that hand bacteria could also aid forensic identification.
It appears that whenever we handle objects, we leave behind unique bacterial communities that could one day sit alongside DNA and fingerprints as part of the forensic toolkit for identifying individuals.