$(window).load(function(){
	$(window).resize(function () { 
		var winW = $(window).width();
		var winH = $(window).height();
		var imgW = 0, imgH = 0;
	
		$('.bg').width(winW).height(winH);
		
		var initW = $('.bg img').width(), initH = $('.bg img').height();
		var ratio = initH / initW;
		
		imgW = winW;
		imgH = winW * ratio;
		
		if(imgH < winH){
			imgH = winH;
			imgW = imgH / ratio;
		}
	
		$('.bg img').width(imgW).height(imgH);
		
	});
	
	$(window).resize();
});