function addImageLayer(className, maskImage) {
  var images = document.getElementsByTagName('img');
	for (var i=0; i<images.length; i++) {
    var image = images[i];
    var classNames = image.className.split(' ');
		for (var j=0; j<classNames.length; j++) {
      if (classNames[j] == className) {
        image.style.backgroundImage = 'url(' + image.src + ')';
        image.src = maskImage;
      }
    }
  }
}