<input type="button" onclick="fn()" >
<script type="text/javascript">

  $(function() {
    fn()
     $("img.lazy").lazyload();
  });

function fn(){


   var img = document.createElement('img');
   img.setAttribute('data-original','bg.jpg')
   img.className='lazy'
   document.body.appendChild(img);
}

</script>

<input type="button" onclick="fn()" value="load Image" >

function fn(){
  var img = $('<img>');
  img.attr('data-original','https://www.google.co.in/logos/doodles/2015/126th-anniversary-of-the-public-opening-of-the-eiffel-tower-4812727050567680-hp.jpg');
  img.attr('class','lazy');
  $(img).appendTo('body');
     setTimeout(function(){
          $("img.lazy").lazyload();
     },100);
 }

<input type="button" onclick="fn()" value="add image">
<img data-src="http://lorempixel.com/400/200/" class="lazyload" />
<script>
    function fn() {
        var img = document.createElement('img');
        img.setAttribute('data-src', 'http://lorempixel.com/400/200/')
        img.className = 'lazyload';
        document.body.appendChild(img);
    }

    fn();
</script>