With CSS 3, now you can stretch background image for a body, div element or other HTML element.

Here are the CSS codes:

html,
body,
div{
    width:100%; 
    height:100%;
    position:relative;
    background: url(img/bg.jpg) no-repeat center center;
    -webkit-background-size:cover; /*for webKit*/
    -moz-background-size:cover; /*Mozilla*/
    -o-background-size:cover; /*opera*/
    background-size:cover; /*generic*/
}