<div id="backgroundImage">
   <img src="img/bodybg.jpg" />
</div>
<div id="onbackgroundbody">
</div>

<style>
html{
width:100%;
height:100%;
margin:0;
padding:0;
}
body{
width:100%;
height:100%;
margin:0;
padding:0;
}
#backgroundImage{
    position: absolute;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    overflow: hidden;
    z-index: -1;
}
#backgroundImage img{
    width: 100%;
    height: 100%;
}
#onbackgroundbody{
    width: 100%;
    height: 100%;
}
</style>