In Identifiable Images of Bystanders Extracted from Corneal Reflections, British psychology researchers Rob Jenkins and Christie Kerr show that recognizable images of the faces of unpictured bystanders can be captured from modern, high-resolution photography by zooming in on subjects' eyes to see the reflections in their corneas. The researchers asked experimental subjects to identify faces captured from these zoomed-in images and found that they were able to do so with a high degree of reliability.
The researchers used 39 megapixel cameras, substantially higher-rez than most people's phone-cameras, but low-cost cameras are making enormous leaps in resolution every day. What's more, the researchers suggest that the determining factor for identifying a face isn't resolution; it's having a viewer who is already familiar with the subject. It's an interesting wrinkle on the problem of information-leakage, and implies that future privacy-filters will have to scrub photos of reflective surfaces (especially eyes) of identifying faces before they're posted.
“In the context of criminal investigations, this could be used to piece together networks of associates, or to link individuals to particular locations. This may be especially important when for categories of crime in which perpetrators photograph their victims. Reflections in the victims eyes could reveal the identity of the photographer. “Also, around 40 million photographs per day are uploaded to Instagram alone, he pointed out. “Faces are among the most frequently photographed objects. Our study serves as a reminder to be careful what you upload. Eyes in the photographs could reveal where you were and who you were with.” Although Jenkins did the study with a high-resolution (39 megapixels) Hasselblad camera, face images retrieved from eye reflections need not be of high quality in order to be identifiable, he said. “Obtaining optimal viewers — those who are familiar with the faces concerned — may be more important than obtaining optimal images.” In addition, “in accordance with Hendy’s Law (a derivative of Moore’s Law), pixel count per dollar for digital cameras has been doubling approximately every twelve months. This trajectory implies that mobile phones could soon carry >39 megapixel cameras routinely.”