I once read the even computers without cameras can secretly somehow be used to film a person through the screen. Could this be true?

Are you thinking of the Samsung televisions which allegedly had a built-in camera?

As many others have pointed out, this is a conspiracy theory.  As is well known, all good lies have a kernel of truth.  This one may have started with the fact that audio loudspeakers can act like microphones (although very inefficient ones).  I could see how a conspiracy theorist would take this truth and by analogy get to the display/camera reversal conspiracy.  Speculation mine.  Interesting, maybe?

I think they need a camera to film you 

It's impossible for computer without camera to picture a guy .

Filming something requires a lens to record motion with. If a computer doesn't have a camera it's not capable of filming. I'm very savvy with computers and have been working with them since the early 80s. I've never found a hidden camera in one. 

It can and does happen where videos are filmed of people without them knowing on devices that do have cameras. This is why the facebook, twitter, and other social networking apps are invasive and unsafe. There is zero reason facebook needs access to *control* a phone or tablet's camera. Access to photos so people can share them, yes. It doesn't need to have control over the microphone and camera so users can share photos and audio but it does. And people just click by giving it permission to invade their privacy when they install or use those apps. 

Use a web browser instead of the app if you insist on supporting cancel culture social networking. It's best to not participate on those networks at all. 

If you use a laptop or tablet or have a smart TV with a built-in camera put a piece of electrical tape over the lens when you're not using it. That way even if an app or someone tries to record you without you knowing they won't get video or photos. They can still get audio unfortunately if the device has a mic.  

Just HOW do you think this could be possible?  A picture is not mentally transmitted. It needs a camera. You can't be filmed if you're not in front of an actual CAMERA.  A computer without a camera cannot film you. 

This is one of the weirder conspiracy theories I've ever heard. 

No, it is impossible for the screen to act as a camera.

I once heard, "A smart man only believes half of what he hears, a wise man knows which half." 

i think it could be true

It is theoretically possible that a camera could be installed inside of the screen undetected, but not probable. For a manufacturer to do this would cost a lot of money, for little benefit. But even as far back as the 90's, when we had those giant CRT monitors, I would joke around about that happening.