<div class="container">
  <img src="https://i.ytimg.com/vi/NHfttfWo-RA/hqdefault.jpg" />

  <img src="https://img.buzzfeed.com/buzzfeed-static/static/2014-07/11/23/enhanced/webdr05/enhanced-32427-1405134811-5.jpg " />

</div>

.container {
  position: relative;
}

.container img {
  width: 100vw;
  object-fit: contain;
  height: 100vh;
  position: absolute;
  top: 0px;
  left: 0px;
  transition: 2s opacity;
}

.container img:nth-child(1) {
  opacity: 1;
}

.container img:nth-child(2) {
  opacity: 0;
}


.container.cross img:nth-child(1) {
  opacity: 0;
}

.container.cross img:nth-child(2) {
  opacity: 1;
}

  var c = document.querySelector('.container');

c.addEventListener('click', function() {
  c.classList.toggle('cross');
});