For years there have been anecdotes from people saying that Facebook secretly uses their phone’s microphone and/or camera for targeted advertising. Joshua Maddux tweeted about a bug he found within the Facebook app. By tapping on a profile picture and slowly sliding it down the screen, you can see his rear camera being accessed on the left hand side. He tested it using five iPhones running iOS 13.2.2.
@facebook #security & #privacy issue. When the app is open it actively uses the camera. I found a bug in the app that lets you see the camera open behind your feed. Note that I had the camera pointed at the carpet.