Comment by ardemue

For the technical side, instead of the historical one: http://responsiveimages.org/

An example from the homepage:

  <picture>
    <source media="(min-width: 40em)" srcset="big.jpg 1x, big-hd.jpg 2x">
    <source srcset="small.jpg 1x, small-hd.jpg 2x">
    <img src="fallback.jpg" alt="">
  </picture>