There are a couple ways to troubleshoot your document camera if there are issues.
Solution: Go to your settings on the left panel of the Visualizer app.
Click on the icon with three circles hooked together.
Adjust the focus to your desire(sometimes you have to play with the focus).
Issue: Not working at all(no response).
Solution: Quit the app-On the track pad us two finger click.
Find and click quit.
Then restart the app.
Issue: Continuous issues and not quitting.
Force quit- click on the apple at the top corner then click force quit.
Restart the app once again to see a response and make sure its working correctly.