CGWeddings: Go to Plugins > Installed Plugins and look for it in the list.
chrisadena: Look for anything else that might be using a different JSON library. It’s a long shot, but do you have the Jetpack JSON API enabled? It’s disabled on my site.
I found the culprit in my site: Use Google Libraries (1.6.1) plug-in. Disabling that allows adding images to posts & pages. Do you have this plug-in loaded chrisadena?
