Toggle image on click

HTML

<script>
    function change() {
   var img1 = "https://farm4.staticflickr.com/3041/2942361043_38a9b3d2ec.jpg",
       img2 = "https://lh3.googleusercontent.com/-mx9FmfkZ8AQ/AAAAAAAAAAI/AAAAAAAAABo/L-smk8cBu-g/s640/photo.jpg";
   var imgElement = document.getElementById('NewImage');
   
   imgElement.src = (imgElement.src === img1)? img2 : img1;
}
</script>
<img src="https://farm4.staticflickr.com/3041/2942361043_38a9b3d2ec.jpg" id="NewImage" onclick ="change();"/>

CSS

#NewImage {
  cursor: pointer;
}