Difficulty 8 out of 10 (10 = most difficult)
This category contains all* of the leaders of the worldwide Catholic Church throughout its history. It is a fairly large and difficult collection, because at the time of this writing, there are no subsets based on recognizability. Brain Bout might create an easier subset in the future. Still, well schooled Catholics, and students of history, might do very well with this challenge.
* At the time of this writing, the category contains 264 entries. A quick check of this subject on Wikipedia returns 266 Popes. Missing images might be the reason for the discrepancy.