Facebook knows how to track you using the dust on your camera lens
Kashmir Hill and Surya Mattu at Gizmodo:
In 2014, Facebook filed a patent application for a technique that employs smartphone data to figure out if two people might know each other. The author, an engineering manager at Facebook named Ben Chen, wrote that it was not merely possible to detect that two smartphones were in the same place at the same time, but that by comparing the accelerometer and gyroscope readings of each phone, the data could identify when people were facing each other or walking together. That way, Facebook could suggest you friend the person you were talking to at a bar last night, and not all the other people there that you chose not to talk to. …
Patents filed by Facebook … show some ingenious methods that Facebook has devised for figuring out that seeming strangers on the network might know each other. One filed in 2015 describes a technique that would connect two people through the camera metadata associated with the photos they uploaded. It might assume two people knew each other if the images they uploaded looked like they were titled in the same series of photos—IMG_4605739.jpg and IMG_4605742, for example—or if lens scratches or dust were detectable in the same spots on the photos, revealing the photos were taken by the same camera.