Retina Images serves different images based on the device being used by the viewer.
Once setup on your website (very simple!) all you have to do is create a high-res version of each image you would like optimized for retina screens and all the work is done for you. You don’t even need to change any <img> tags (providing they have a height or width).
This should be compatible with OSC2.2+ and sites that are viewport optimized.
This is based on the work done by Jeremy Worboys over at http://retinaimag.es/