In iOS 8, it's possible for the camera to be disabled for any given app; in iOS 7, this was only possible in certain regions (e.g. China).
If the camera is disabled, and someone launches the Camera plugin to capture an image from the camera, they'll just get the camera UI with a black screen, and no indication that the camera permission is disabled for the app. A better UX would be to show the user a prompt indicating that the camera permission is disabled, and (on iOS 8) providing a button to take them to the Settings app to change it.
As of iOS 7, there's a new API to test whether the app has access to capture the desired media type: