FWIW, you can do content negotiation on the client side with the HTML5 picture element: http://www.html5rocks.com/en/tutorials/responsive/picture-element/#toc-

FWIW, you can do content negotiation on the client side with the HTML5 picture element: http://www.html5rocks.com/en/tutorials/responsive/picture-element/#toc-file-type http://www.html5rocks.com/en/tutorials/responsive/picture-el... If a browser doesn't support that, it's probably not going to support the image format you're trying to negotiate anyway. In that case it's just going to fall back to the enclosed default img which is exactly what you'd want.