$(function() {
	var theWindow = $(window),
	    $bg = $("#bg"),
	    aspectRatio = $bg.width() / $bg.height();
	function resizeBg() {
		if ( (theWindow.width() / theWindow.height()) < aspectRatio ) {
		    $bg
		    	.removeClass()
		    	.addClass('bgheight');
		} else {
		    $bg
		    	.removeClass()
		    	.addClass('bgwidth');
		}
	}
	theWindow.resize(function() {
		resizeBg();
	}).trigger("resize");
});