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HTML

              
                <video id="monitor" autoplay style="display: none; width: 320px; height: 240px;"></video>

<div id="canvasLayers"  width="320" height="240"  style="position: relative; left: 0px; top: 0px;">
<canvas id="videoCanvas" width="320" height="240" style="z-index: 1; position: absolute; left:0px; top:0px;"></canvas>
<canvas id="layer2"     width="320" height="240" style="z-index: 2; position: absolute; left:0px; top:0px; opacity:0.5;"></canvas>
</div>
<canvas id="blendCanvas" style="display: none; position: relative; left: 400px; top: 0px; width: 320px; height: 240px;"></canvas>
<div id="messageError"></div>
<div id="messageArea" style="position: relative; left: 0px; top: 270px;">Messages will be displayed here.</div>


              
            
!

CSS

              
                		body 
		{
			font-family: Monospace;
			font-weight: bold;
			background-color: #fff;
			margin: 5px;
			overflow: hidden;
		}
              
            
!

JS

              
                /**
 * Provides requestAnimationFrame in a cross browser way.
 * http://paulirish.com/2011/requestanimationframe-for-smart-animating/
 */

if (!window.requestAnimationFrame) {

  window.requestAnimationFrame = (function() {

    return window.webkitRequestAnimationFrame ||
      window.mozRequestAnimationFrame ||
      window.oRequestAnimationFrame ||
      window.msRequestAnimationFrame ||
      function( /* function FrameRequestCallback */ callback, /* DOMElement Element */ element) {

        window.setTimeout(callback, 1000 / 60);

      };

  })();

}

navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
window.URL = window.URL || window.webkitURL;

var camvideo = document.getElementById('monitor');

if (!navigator.getUserMedia) {
  document.getElementById('messageError').innerHTML =
    'Sorry. <code>navigator.getUserMedia()</code> is not available.';
}
navigator.getUserMedia({
  video: true
}, gotStream, noStream);

function gotStream(stream) {
  if (window.URL) {
    camvideo.src = window.URL.createObjectURL(stream);
  } else // Opera
  {
    camvideo.src = stream;
  }

  camvideo.onerror = function(e) {
    stream.stop();
  };

  stream.onended = noStream;
}

function noStream(e) {
  var msg = 'No camera available.';
  if (e.code == 1) {
    msg = 'User denied access to use camera.';
  }
  document.getElementById('errorMessage').textContent = msg;
}

// assign global variables to HTML elements
var video = document.getElementById('monitor');
var videoCanvas = document.getElementById('videoCanvas');
var videoContext = videoCanvas.getContext('2d');

var layer2Canvas = document.getElementById('layer2');
var layer2Context = layer2Canvas.getContext('2d');

var blendCanvas = document.getElementById("blendCanvas");
var blendContext = blendCanvas.getContext('2d');

var messageArea = document.getElementById("messageArea");

// these changes are permanent
videoContext.translate(320, 0);
videoContext.scale(-1, 1);

// background color if no video present
videoContext.fillStyle = '#005337';
videoContext.fillRect(0, 0, videoCanvas.width, videoCanvas.height);

var buttons = [];

var button1 = new Image();
button1.src = "https://stemkoski.github.io/Three.js/images/SquareRed.png";
var buttonData1 = {
  name: "red",
  image: button1,
  x: 320 - 110,
  y: 10,
  w: 100,
  h: 80
};
buttons.push(buttonData1);

var button2 = new Image();
button2.src = "https://stemkoski.github.io/Three.js/images/SquareGreen.png";
var buttonData2 = {
  name: "green",
  image: button2,
  x: 10,
  y: 10,
  w: 100,
  h: 80
};
buttons.push(buttonData2);

/*
var button3 = new Image();
button3.src ="https://stemkoski.github.io/Three.js/images/SquareBlue.png";
var buttonData3 = { name:"blue", image:button3, x:320 - 32 - 10, y:10, w:32, h:32 };
buttons.push( buttonData3 );
*/
// start the loop				
animate();

function animate() {
  requestAnimationFrame(animate);

  render();
  blend();
  checkAreas();
}

function render() {
  if (video.readyState === video.HAVE_ENOUGH_DATA) {
    // mirror video
    videoContext.drawImage(video, 0, 0, videoCanvas.width, videoCanvas.height);
    for (var i = 0; i < buttons.length; i++)
      layer2Context.drawImage(buttons[i].image, buttons[i].x, buttons[i].y, buttons[i].w, buttons[i].h);
  }
}

var lastImageData;

function blend() {
  var width = videoCanvas.width;
  var height = videoCanvas.height;
  // get current webcam image data
  var sourceData = videoContext.getImageData(0, 0, width, height);
  // create an image if the previous image doesn�t exist
  if (!lastImageData) lastImageData = videoContext.getImageData(0, 0, width, height);
  // create a ImageData instance to receive the blended result
  var blendedData = videoContext.createImageData(width, height);
  // blend the 2 images
  differenceAccuracy(blendedData.data, sourceData.data, lastImageData.data);
  // draw the result in a canvas
  blendContext.putImageData(blendedData, 0, 0);
  // store the current webcam image
  lastImageData = sourceData;
}

function differenceAccuracy(target, data1, data2) {
  if (data1.length != data2.length) return null;
  var i = 0;
  while (i < (data1.length * 0.25)) {
    var average1 = (data1[4 * i] + data1[4 * i + 1] + data1[4 * i + 2]) / 3;
    var average2 = (data2[4 * i] + data2[4 * i + 1] + data2[4 * i + 2]) / 3;
    var diff = threshold(fastAbs(average1 - average2));
    target[4 * i] = diff;
    target[4 * i + 1] = diff;
    target[4 * i + 2] = diff;
    target[4 * i + 3] = 0xFF;
    ++i;
  }
}

function fastAbs(value) {
  return (value ^ (value >> 31)) - (value >> 31);
}

function threshold(value) {
  return (value > 0x15) ? 0xFF : 0;
}

// check if white region from blend overlaps area of interest (e.g. triggers)
function checkAreas() {
  for (var b = 0; b < buttons.length; b++) {
    // get the pixels in a note area from the blended image
    var blendedData = blendContext.getImageData(buttons[b].x, buttons[b].y, buttons[b].w, buttons[b].h);

    // calculate the average lightness of the blended data
    var i = 0;
    var sum = 0;
    var countPixels = blendedData.data.length * 0.25;
    while (i < countPixels) {
      sum += (blendedData.data[i * 4] + blendedData.data[i * 4 + 1] + blendedData.data[i * 4 + 2]);
      ++i;
    }
    // calculate an average between of the color values of the note area [0-255]
    var average = Math.round(sum / (3 * countPixels));
    if (average > 50) // more than 20% movement detected
    {
      //console.log("Button " + buttons[b].name + " triggered."); // do stuff
      messageArea.innerHTML = "<font size='+4' color=" + buttons[b].name + "><b>Button " + buttons[b].name + " triggered.</b></font>";
      
      op(buttons[b].name);
      
    }
  }
}

function op(n) {
  console.log(n);
  //window.open("https://www.w3schools.com");
}
//,
              
            
!
999px

Console