<img src="yourimage" width="100%" height="100%" style="z-index:0"/>

<div style="width:100%; z-index:0; height:100%; background: url(1pximage.gif)"></div>

body {
    background-size: 100%;
}

$(function(){

   $(window).resize(function(){

      var windowW = $(window).width();
      var windowH = $(window).height();

      //Using above variables you can deside the size of the background image to be set
   }).resize();//Trigger the resize event on page load.
});