kullanabileceğin html kod var
<body background="arkaplan.jpg">
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;
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;
background-image: url('resim.jpg');