Thanks for the catch. Added a source element but Medium doesn't let you link photos so I credited it in the sentence before: http://cl.ly/image/0G0Q2S2D2h3L
The word "illustration" in the sentence above it does link to the The Oatmeal, but you're right it should probably be clearer.
Yep, just noticed. I clicked on that link originally, but it didn't load for some reason.