title: Take photo when face detected
body: <p>I have the following code and i want to automatic take only one photo when a face is detected.
  I have achieve to automatic take photo but it takes many photos without time to process them because it continuously detect the face. How can i make it to search every x minutes to find a face or every x minutes to take photo? Thank you in advance.</p>
  
  <pre><code>FaceDetectionListener faceDetectionListener
  = new FaceDetectionListener(){
  
      @Override
      public void onFaceDetection(Face[] faces, Camera camera) {
  
          if (faces.length == 0){
              prompt.setText(" No Face Detected! ");
          }else{
              //prompt.setText(String.valueOf(faces.length) + " Face Detected :) ");
                try{
                  camera.takePicture(myShutterCallback,myPictureCallback_RAW, myPictureCallback_JPG);
  
                 }
                 catch(Exception e){
  
                 }
          }
  
  
      }};
  </code></pre>