Full Background

Für ganze Website:

html { 
	background: url(img/bg.jpg) no-repeat center center fixed; 
	-webkit-background-size: cover;
	-moz-background-size: cover;
	-o-background-size: cover;
	background-size: cover;
}

Für einzelne divs:

.class { 
	background: url(img/bg.jpg) no-repeat center center scroll; 
	-webkit-background-size: cover;
	-moz-background-size: cover;
	-o-background-size: cover;
	background-size: cover;
}