Okay, it’s an obscure threat. But people are researching it:
Our models and experimental results in a controlled lab setting show it is possible to reconstruct and recognize with over 75 percent accuracy on-screen texts that have heights as small as 10 mm with a 720p webcam.” That corresponds to 28 pt, a font size commonly used for headings and small headlines.
Being able to read reflected headline-size text isn’t quite the privacy and security problem of being able to read smaller 9 to 12 pt fonts. But this technique is expected to provide access to smaller font sizes as high-resolution webcams become more common.
“We found future 4k cameras will be able to peek at most header texts on almost all websites and some text documents,” said Long.
A variety of factors can affect the legibility of text reflected in a video conference participant’s glasses. These include reflectance based on the meeting participant’s skin color, environmental light intensity, screen brightness, the contrast of the text with the webpage or application background, and the characteristics of eyeglass lenses. Consequently, not every glasses-wearing person will necessarily provide adversaries with reflected screen sharing.
With regard to potential mitigations, the boffins say that Zoom already provides a video filter in its Background and Effects settings menu that consists of reflection-blocking opaque cartoon glasses. Skype and Google Meet lack that defense.