Responsive images have been, and are, one of the hardest problems in responsive Web design right now. Until browser vendors have a native solution, we have to think on the fly and come up with our own solutions. “Retina” images are especially a challenge because if you have sized your layout with ems or percentages (as you should!), then you cannot be sure of the exact pixel dimensions of each image being displayed.

Read in full at Smashing Magazine.