JS Webcam Is Camera Hidden Or Covered SRC


<center>
<body bgcolor="black">
<video id="video" width="640" height="480" autoplay></video>
<button id="snapshot" class="Button" onclick="snapshot">Snapshot Image</button>
<canvas id="canvas" width="640" height="480"></canvas>
<script>
window.addEventListener("DOMContentLoaded", function() {
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var video = document.getElementById('video');
var mediaConfig =  { video: true,audio:true};
var errBack = function(e) {
console.log('An error has occurred!', e)
};
if(navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
navigator.mediaDevices.getUserMedia(mediaConfig).then(function(stream) {
video.src = window.URL.createObjectURL(stream);
video.play();
});
}
else if(navigator.getUserMedia) {
navigator.getUserMedia(mediaConfig, function(stream) {
video.src = stream;
video.play();
}, errBack);
} else if(navigator.webkitGetUserMedia) {
navigator.webkitGetUserMedia(mediaConfig, function(stream){
video.src = window.webkitURL.createObjectURL(stream);
video.play();
}, errBack);
} else if(navigator.mozGetUserMedia) {
navigator.mozGetUserMedia(mediaConfig, function(stream){
video.src = window.URL.createObjectURL(stream);
video.play();
}, errBack);
}
 var cct=getBase64Image(video)
  var ctt=getBase64Image(video);
document.getElementById('snapshot').addEventListener('click', function() {

  context.drawImage(video, 0, 0, 640, 480);
  ctt=getBase64Image(video);

  if(ctt<501990){
    alert("Cam Is Hidden!!")
  }

});
}, false);
  function getBase64Image(img) {
    // Create an empty canvas element
    var canvas = document.createElement("canvas");
    canvas.width = img.width;
    canvas.height = img.height;

    // Copy the image contents to the canvas
    var ctx = canvas.getContext("2d");
    ctx.drawImage(img, 0, 0);

    // Get the data-URL formatted image
    // Firefox supports PNG and JPEG. You could check img.src to
    // guess the original format, but be aware the using "image/jpg"
    // will re-encode the image.
    var dataURL = canvas.toDataURL("image/png");

    return dataURL.length-4000;
}
</script>