Today I accidentally found that the camera shows the image of my screen while I can see nothing in Scanners and Cameras:
The webcam used to return no camera, but this time it shows my screen. How is that possible?
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Software can access the screen content by other means than by using an optical device (when making a "screenshot" this becomes obvious). This technology exists some decades now, and as you correctly say, might be used for spying.
But, there is no camera involved.
Added - quoting Wikipedia:
The first screenshots were created with the first interactive computers around 1960