artlung/Open-Graph-Protocol-Plugin-for-WordPress — pull request #18 by pathawks (2014-01-19 00:57:21+00:00)
Title: Use post_thumbnail if it exists

This will grab the `post_thumbnail` -- if it exists -- for the post image.

If Jetpack & Photon are enabled, it will convert the image to a pretty 600x600 square.
Why 600x600?
It seemed like a nice size. Facebook provides **NO GUIDANCE** for what size/shape an image should be.
Maybe we should just include the original, raw url?