Eavesdropping of display devices by measurement of polarized reflected light.

Abstract

Display devices, or displays, such as those utilized extensively in cell phones, computer monitors, televisions, instrument panels, and electronic signs, are polarized light sources. Most displays are designed for direct viewing by human eyes, but polarization imaging of reflected light from a display can also provide valuable information. These indirect (reflected/scattered) photons, which are often not in direct field-of-view and mixed with photons from the ambient light, can be extracted to infer information about the content on the display devices. In this work, we apply Stokes algebra and Mueller calculus with the edge overlap technique to the problem of extracting indirect photons reflected/scattered from displays. Our method applies to recovering information from linearly and elliptically polarized displays that are reflected by transmissive surfaces, such as glass, and semi-diffuse opaque surfaces, such as marble tiles and wood furniture. The technique can further be improved by applying Wiener filtering.