... and your camera lens is always exposed to dust and can be damaged by objects. No good idea. You could also propose he should take a separate flashlight with him, that would be as helpful.

I like the idea of an option menu. Maybe it could have an open plugin like architecture. So that other apps can add a button to it.
So one could choose what he wants to do with the camera when the cover is opened. The buttons could be: Start default foto/video application, start mbarcode and a flashlight togglebutton.