Perfect Full Page Background Image http://css-tricks.com/perfect-full-page-background-image/

main.css

html,
body {
  width: 100%;
  height: 100%;
}

/* div */.body { 
  background: url(images/bg.jpg) no-repeat center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
  filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src='.myBackground.jpg', sizingMethod='scale');
  -ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='myBackground.jpg', sizingMethod='scale')";
}