Official RICG Web sites
- http://responsiveimages.org/ - contains links to the specs, repos, etc
- http://ricg.io/ - contains feature status
Articles explaining the various use-cases and solutions:
- https://dev.opera.com/articles/native-responsive-images/ - An explainer article I wrote.
- https://dev.opera.com/articles/responsive-images/ - A "cookbook" with all the various permutations of use-cases, by Andreas Bovens.
- http://ericportis.com/posts/2014/srcset-sizes/ - An awesomely funny article explaining srcset and sizes.
- http://www.smashingmagazine.com/2014/05/14/responsive-images-done-right-guide-picture-srcset/ - An explainer by Eric Portis.