Probably notice that your webcam light comes on only once every ten minutes, or that your network traffic is consistent with one picture every ten minutes.

Isn't this site for nerds?

You can see the work log online that contains all the screenshots and most probably camera shots too (never had to use it so I'm not 100% sure).

I think the way to know that your camera is on is to look at the little LED next to your camera and hoping UpWork didn't find a way around it.

Get a camera where the activity LED turns on when camera is active.