$(document).ready(function() {
   // put all your jQuery goodness in here.width
   var windowWidth = $(window).width();
   
   if(windowWidth <= 1280)
   {
   		var origWidth = $('.main-img').width();
   		var origHeight = $('.main-img').height();
   		$('.main-img').width(origWidth * 0.65);
   		$('.main-img').height(origHeight * 0.65);
   		
   }
 });