We'll create fresh WordPress site with Simple Responsive Images installed. You have 20 minutes to test the plugin after that site we'll be deleted.
This plugin generate images with attributes for the responsive images in your content.
Choose the breakpoints and the sizes associated.
The next images you will insert and the elements generated with the wp_attachement functions will begenerated with the right attributes.
Contribute on https://github.com/Rahe/Simple-responsive-images
Based on http://www.grahambird.co.uk/lab/doubletake/ for javascript