Fond d'écran 100%

#bg {
	height: 100%;
	left: 0;
	position: fixed;
	top: 0;
	width: 100%;
}
#bgImage { width:100%; height: 100%; }
#wrapper { position:relative; }
  <body>
    <div id="bg"><img src="backbg.jpg" id="bgImage" alt=""/></div>
    <div id="wrapper">
    </div>
  </body>

CSS3

background-size: 100% 100%;