My external webcam, on a Mac running OS X, has been taking a photo when an application is opened. This practice continued when I changed webcams.
The webcam’s light comes on, its lens cover opens, and it flashes.
With newer, faster, computers with internal webcams, it’s possible that users would not notice the flash.
Being concerned about surveillance, I searched for other people who have had this experience. It turns out that Adobe Flash Player routinely allows third-party sites to operate one’s webcam, and even store data on one’s computer - unless these permissions are explicitly turned off in the settings.
When I went to the Flash settings webpage, I found that Flash had authorized such use of the webcam, WITHOUT ASKING – ie, that is the Default.