Use of photos in large auditoriums

Hi
I am giving lectures in large auditoriums. The projectors are of very varying quality. My illustrating graphs and text are no problem, because I use a lot of contrast (i.e. black and white), BUT when I want to show "real" life using photographs I am in deep trouble. You just cant see the nice details that are so important. This is of cause due to the details beeing in the shadows (or the like).
I do not have any possibility of turning off the light in the room (it is dimmed already) and profiling is not an option (I am using 5 - 6 different locations). What do I do. Is there any "formula" for editing photographs for this kind of presentations. The obviuos solution is to shoot for the interesting details in the middle or high lights, but again this is not always an option.
Hoping that someone out there can help me.
Jorgen