All you have done thus far is basically housekeeping. You will now access the FaceDetector API by which you will, well, detect the face in the image. You will disable tracking for now, as you only want to detect the face at this stage.

Note that on its first run, the Play Services SDK will take some time to initialize the Faces API. It may or may not have completed this process at the time you intend to use it. Therefore, as a safety check, you need to ensure its availability before using it. In this case, you will show a simple dialog to the user if the FaceDetector is not ready at the time the app is run.

Also note that you may need an internet connection as the SDK initializes. You also need to ensure you have enough space, as the initialization may download some native library onto the device:

// Create a FaceDetector
val faceDetector = FaceDetector.Builder(applicationContext).setTrackingEnabled(false)
        .build()
if (!faceDetector.isOperational) {
    AlertDialog.Builder(this)
            .setMessage("Could not set up the face detector!")
            .show()
    return
}