Player face images should be in PNG format and 157px wide x 200px tall. If the head takes up the full 200px then it can look a bit cramped in-game. Most packs I have seen created by users leave the top 4px of the image blank/transparent so that the top of head isn't too close to other elements on the screen.
I'll get us started: For the benefit of batdad, here's a Tony Hand image:

tony_hand_15_8_1967.png