I didn't knew about srcset as a W3C standard though: <a href="http://www.w3.org/html/wg/drafts/srcset/w3c-srcset/" rel="nofollow">http://www.w3.org/html/wg/drafts/srcset/w3c-srcset/</a> , thx! It seems to exist on imageResizer also, it's a .Net package for image resizing, that works like the API described (different syntax though)