Automattic/jetpack — pull request #418 by rowatt (2014-03-24 22:11:00+00:00)
Title: Fix PHP notice in Jetpack_PostImages::from_attachment method

Add logic to cope with images in posts with protocol independent and root relative urls. The URLs returned are always absolute, using WP_HOME if the image src in the post was a root relative URL. This method is used by the Jetpack OpenGraph functions, and the og:image property should be absolute (apparently... though the documentation does not seem to explicitly state this).