An Image histogram can be a useful tool when evaluating the exposure of your photographs. A quick look at the histogram after you took a photo might help you find out, if your photo is overexposed or underexposed.
A kiosk app is usually an app that forces an Android device to be used for a single specific purpose, preventing the user from exiting it or from using device features outside of the app itself.
Camera2 API is the newer API for controlling camera devices on Android. Although it is often used in cam apps from an Activity or Fragment, there might be some use cases where you want to acquire and process camera frames in the background while other apps are in the foreground.