Live Camera to Screen
Using live cameras on screen is very useful with a very large audience that have limited view of the stage. It is also a useful technique for relaying a presentation to additional overflow rooms.
Using a single camera connected directly to your projector or screen will do the job but the camera must be fixed or a very skilled cameraman that can be relied upon to always have an interesting shot! A better alternative is to use 2 or more cameras and a Video Mixer. This way an opperator can select the camera with the best shot at any given time and show this on screen whilst other cameras re-position.
Other, less labor intensive options are remote head cameras. These are video cameras with motorised yolks and several are connected and controlled from a central position by a single technician.