As hinted at in a few of the links I referenced, Pillow was the culprit. I installed 2.2.1 using pip install Pillow
and although the install finished successfully, a simple test failed such as: from PIL import Image
Upon viewing this post: Installing Pillow for Python on Windows
I went ahead and used the executable installer: http://www.lfd.uci.edu/~gohlke/pythonlibs/#pillow
I was able to successfully perform the above test.
With Pillow successfully installed and tested, the cache management command, plcache
, finally worked, the "cache" folder was filled, and the thumbnails are now shown in my site!