Css Ve Javascript İle Tam Ekran Arkaplan Resmi Yapmak

<img alt="Arkaplan" src="img/bg.png" id="bg" />

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.js"></script>
<script>
$(document).ready(function() {


 var bgImage = $('#bg');		
 
    function resizeImg() {
      var imgwidth = bgImage.width(),
		   imgheight = bgImage.height(),
		   winwidth = $(window).width(),
		   winheight = $(window).height(),
		   widthratio = winwidth / imgwidth,
		   heightratio = winheight / imgheight,
		   widthdiff = heightratio * imgwidth,
		   heightdiff = widthratio * imgheight;
 
      if(heightdiff>winheight) {
        bgImage.css({
          width: winwidth+'px',
          height: heightdiff+'px'
        });
      } else {
        bgImage.css({
          width: widthdiff+'px',
          height: winheight+'px'
        });		
      }
	 
	 $("#bg").show();
	  
    } 
    resizeImg();
    $(window).resize(function() {
      resizeImg();
    }); 



});

</script>

#bg{
	position:absolute;
	top:0;
	left:0;
	z-index:-10;
	overflow: hidden;
    width: 100%;
	display:none;
	}

#body {
background-color:#ffffff;
}