Unfortunately, Apple does not provide low level API for camera control on iPhone. Apple provides UIImagePickerController, but it does not allow us to access camera in low level either. To do what they want, some people found there is private frameworks that are not publicly available.
The PhotoLibrary framework, one of the private frameworks, has a class called CameraController and it provides interface for camera control. Since it is not available in the iPhone SDK, someone who wants to use it have to some works on it.
I have to dig more on this topic....
iflickr found in google code is one of examples on the web, which uses CameraController class.(http://code.google.com/p/iflickr/)