resize image based on browser resize (and keeping dimensions)

Google recently added backgrounds to it's home page .. Like it or hate it, it's got the ability to resize 开发者_开发百科the background image while keeping the same proportions as the browser window resizes...

Anyone know of any jQuery to do that?

Width is set to a percentage.

$(window).resize(function() {
   $('#imgContainer').width( $(this).width() );
                     .height( $(this).height() );
});