WordPress 4.4 just announced few important features. One thing that caught my attention is this: “Responsive Images”.
How it works
WordPress automatically creates several sizes of each image uploaded to the media library. By including the available sizes of an image into a
srcset attribute, browsers can now choose to download the most appropriate size and ignore the others—potentially saving bandwidth and speeding up page load times in the process.
This is a must have feature for Percussion CM1.
Source for more information: https://make.wordpress.org/core/2015/11/10/responsive-images-in-wordpress-4-4/
WordPress is now smarter at displaying appropriate image sizes on any device, without you having to make any modifications to your theme.