How Apple.com will serve retina images to new iPads « Cloud Four:

One of the more interesting questions raised by the new iPad and its retina display is whether or not web sites should deliver higher resolution images when there is no way to know the connection speed. AppleInsider found that Apple.com is being prepped to deliver high-res images and documented how you can test it in Safari on your desktop.

As you can imagine given my research on responsive images, I was keenly interested to see what approach Apple took.

What they’ve chose to do is load the regular images for the site and then if the device requesting the page is a new iPad with the retina display, they use javascript to replace the image with a high-res version of it.