When you are limited to using an inbuilt static camera on your iMac its no wonder you stay away from Skype for demo purposes.
This is the HD camera in my 4 year old iMac and its appalling. Apple sell you great all in one computers like the 27″ iMac but compromise on the build of the in built camera.
This is the Logitech c920 HD camera (£59 on Amazon) that works with the iMac as long as you use an APP called WEBCAM SETTINGS (£7.99 Apple APP store). I am using Mojave on OS 10.14.3 and it works fine. Dont be put off by the bad reviews and its also 5 years old.
Logitech have their own app for the camera but it does not allow you the most important feature in WEBCAM SETTINGS the ability to adjust the GAIN. In advanced settings you can also focus the C920 manually. The best news is portability, your no longer stuck with a static camera position, you also get very useful 1.5m of cable.
The Logitech c920 is a far superior picture in all ways the main one having the control over the gain and the ability to set manual focus and a good white balance.
I must thank this You Tubber Andrew Strugnell for showing me how good the c920 is on an iMac and remember this You Tube video is 7 years old.