Design Shack has written a nice tutorial on Focal Point: Intelligent Cropping of Responsive Images, which is going to look at a fascinating little framework that allows you to not only automatically resize your images when the viewport changes, but also crop the images with a specific important focal point in mind. Amazingly enough, it does all this with pure CSS.
Read more at http://www.webappers.com/#uxmU7H8kKAJ99qKO.99