$(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");
		});