http://camfoot.com/plugins/auto/image_responsive/v7.3.0/javascript/picturefill.js
https://wellcome.ac.uk/sites/all/themes/corp_base/assets/js/libraries/picturefill.js
https://waddell.com/Scripts/WDDLWEB/polyfills/picturefill.js
http://www.truro-penwith.ac.uk/js/vendor/picturefill.js
http://www.mieux-etre.org/plugins/auto/image_responsive/v7.1.0/javascript/picturefill.js