You may be able to add the UIImageView as a subview of the main window directly instead of the UIImagePicker, it may work better. Just make sure to add them in the right order, or call
[window bringSubviewToFront:imageView];
after the camera is up.
If you want to handle touches on the UIImageView you could just add the UIImageView as a subview of a normal fullscreen View with a transparent background, and add that to the window instead, with a normal UIViewController subclass that you can use to handle the touch events.