If you are in the video conference, you can switch off the transmission of your camera by clicking on the camera symbol at the bottom of the conference.
If your video is not broadcast, the camera icon is crossed out. In this case, no other participant can see you.
By clicking on the symbol again, your camera transmission will be reactivated.
Other users cannot turn your camera on or off, not even the moderator of the video conference. 

This setting (camera switched off) is recommended for all participants during larger conferences with a higher number of participants so that the bandwidth is kept as low as possible.