It need "FaceChaser for Arduino". It need libraries openCV, video, serial, for processing too.

FaceChaser for Processing3

import gab.opencv.*;
import processing.video.*;
import java.awt.*;

Capture video;
OpenCV opencv;

import processing.serial.*;

Serial myPort;  // Create object from Serial class
int val;        // Data received from the serial port


void setup() {
  size(960, 720);
  println(Capture.list());
  video = new Capture(this,width/3,height/3,Capture.list()[20]);
  opencv = new OpenCV(this, width/3, height/3);
  opencv.loadCascade(OpenCV.CASCADE_FRONTALFACE);  
  video.start();
  
  String portName = Serial.list()[0];
  println(portName);
  myPort = new Serial(this, portName, 9600);
 
  
  
}

void draw() {
  scale(3);
  opencv.loadImage(video);
  image(video, 0, 0 );

  noFill();
  stroke(0, 255, 0);
  strokeWeight(1);
  Rectangle[] faces = opencv.detect();
  //println(faces.length);
  
  int[] x = new int[20];
  int[] y = new int[20];
  boolean exist = false;
  
  for (int i = 0; i < faces.length; i++) {
    x[i] = faces[i].x + faces[i].width/2;
    y[i] = faces[i].y + faces[i].height/2;
    println(i,x[i] , y[i]); 
    exist = true;
    rect(faces[i].x, faces[i].y, faces[i].width, faces[i].height);
  }
  if(exist == true){
      if( x[0] > 170){
        myPort.write('H');
        println('H');
      }else if(x[0] < 130){
        myPort.write('L');
        println('L');
      } else{
        myPort.write('C');
        println('C');
      }
  } else {
   myPort.write('N');
   println('N');
  }
  
}



void captureEvent(Capture c) {
  c.read();
}


void sendCommand(){

}