How to ensure you have a less problematic video:
Correct Lighting: Make sure you aren’t in front of a window or around bright lights that can obscure the view of your face in the video. Makfe sure you have adequate lighting. Don’t take the exam in the dark with the screen as the only lighting.
https://www.lifesize.com/en/video-conferencing-blog/video-conferencing-lighting-solutions
Posture and Positioning: Make sure you are properly positioned in front of the screen. Begin and end your quiz in the same place; don’t start it sitting at a table and then move to lie down on the bed. You will be flagged for moving, your lighting may change and obscure your face, etc…
Facial Visibility: Don’t wear sunglasses, low brimmed hats, scarves, or hoodies that may obscure your face. Your face needs to be visible at all times during the quiz.