If you see the below image during your pre-exam webcam check, it is because of a privacy setting that is enabled in your camera's software utility. Please be aware that this same image will be all that is displayed to your instructor when they review your video.
Several cameras have privacy settings like this, but the most common are found on Lenovo computers. To disable this setting on a Lenovo computer, go to "Lenovo Settings" > "Configure Camera Settings" and toggle the setting from "Private" to "Normal." If "Lenovo Settings" is not found, try "Lenovo Vantage." Once found, go to “My Device Settings” > Display & Camera > Camera to toggle the privacy mode setting from or “ON” to “OFF.”
Please be aware that changing privacy settings on the Windows operating system will not help resolve this problem. Rather, it must be done only via the "Lenovo" or "Lenovo Vantage" utility. Restarting the computer after making this change is recommended.
Please refer to your manufacturer's user guide for further assistance.
Some additional troubleshooting steps that might help (for Lenovo computers) are here: https://www.techjunkie.com/lenovo-webcam-not-working-issue/
Some computers have a physical on/off webcam switch on the side of the laptop. If your computer has such a switch, be sure to set it to "on."