Do not share! Invisible light beacons for signaling preferences to privacy-respecting cameras

The ubiquity of cameras in today's world has played a key role in the growth of sensing technology and mobile computing. However, on the other hand, it has also raised serious concerns about privacy of people who are photographed, intentionally or unintentionally. The popularity of publishing pictures in social networks adds to the concern that the photographed user has the least control over his/her picture. In this paper, we present the design, implementation and evaluation of "invisible light beacons" where privacy preferences of photographed users are communicated to photographing cameras. Particularly, we explore a design where the beacon transmitters are worn by users on their eyewear and transmit a privacy code through ON-OFF patterns of light beams from IR LEDs. The beacons are received and decoded by a camera and mapped to different privacy preferences corresponding to that code. Based on the experimental evaluation of thousands of data points using our prototype implementation we show that the detection accuracy of a known privacy code is greater than 98%, and error rate of communicating a random stream of bits over an indoor IR-camera channel is within 7% at packet level and of the order of 10^-3 at bit level.