PLOS One

Investigators already use images from security cameras and photographs snapped by bystanders to solve crimes, but a new study suggests criminal evidence could actually be found in photos that capture the reflections in bystanders' eyes.

Researchers from the University of York and the University of Glasgow used high-resolution photography to zoom in on faces and eyes in photos to see what's reflected back through bystanders' corneas, and found that observers were able to identify the images accurately, despite their low resolution.

"The pupil of the eye is like a black mirror," research leader Rob Jenkins of the University of York's Department of Psychology said in a statement. "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. Our findings thus highlight the remarkable robustness of human face recognition, as well as the untapped potential of high-resolution photography."

The scientists used a 39-megapixel digital camera to shoot high-resolution passport-style photographs of eight individuals in front of staged "witnesses," making sure those "witnesses" were reflected in the individuals' corneas.

Then the scientists showed zoomed-in versions of the witnesses to a control group tasked with matching these highly pixelated faces to normal, in-focus profile pictures. The results showed that the bystanders' faces -- even when very pixelated -- were recognizable.

The team's findings, published in the journal PLOS One under the title "Identifiable Images of Bystanders Extracted from Corneal Reflections," reaffirmed previous research that showed familiar faces could be identified even if the resolution was "as low as 7x10 pixels."

When used as part of forensic evidence, these reflections could yield additional information about perpetrators of crimes. Say someone snapped a shot of a robbery with a cell phone. Images that captured bystanders' faces could be blown up and examined for clues. The technique could also be valuable in situations where victims are photographed, such as hostage taking, the researchers say.

Mobile phones, of course, are continuously upping the quality of their digital cameras, which could be good news for those collecting evidence. The Nokia 808 PureView, for one, already boasts a 41-megapixel camera, making it, says CNET's Lynn La, "a phone that has so many megapixels, its megapixels have megapixels."