Pure CSS solution to retina images with a single file

Problem: You have an image and want it to display well in browsers on a high DPI display. There are many ways to do this, some of them more complicated than others. My requirements were pretty simple: I want to be able to publish “retina” images with default markdown syntax I prefer images to be blurry on non-high DPI screens, they are blurry anyway so what’s the harm. I do not care about wasted bandwidth by sending retina assets to clients with standard definition screens.