There is a new attribute for the img tag that allows you to add a retina src attribute, namely srcset. No javascript or CSS needed, no double loading of images.
<img src="https://stackoverflow.com/questions/13744542/low-res.jpg" srcset="https://stackoverflow.com/high-res.jpg 2x">
Browser Support: http://caniuse.com/#search=srcset
Other Resources:
- WebKit release post
- W3C documentation for srcset
- good explanation about why and how to use srcset
- Chris Coyer’s post for more good info