body{
            background-position:center; 
            background-repeat:no-repeat; 

}

div#div1{ 
position:fixed; 
top:0; 
left:0; 
bottom:0; 
right:0; 
z-index:-1; 
} 
div#div1 > img { 
height:100%; 
width:100%; 
border:0; 
} 


<div id="div1"><img src="http://www.mamicode.com/image/a203d57edee4a77d41102c968608e3b2.jpg" /></div>