var domElement = document.getElementById('new2');
domElement.width = domElement.naturalWidth * 0.5;
<p><b>Actual image </b></p>
<img id="new" src="http://static.sportskeeda.com/wp-content/uploads/2014/08/wrestling-india-cwg-2014-1407343871-2252471.jpg">
<p><b>50% reduced image </b></p>
<img id="new2" src="http://static.sportskeeda.com/wp-content/uploads/2014/08/wrestling-india-cwg-2014-1407343871-2252471.jpg" >
<p>Note: both image sources are same.