Thought some may find this little cheaty technique helpful,
I can't paint faces -or any detailed image for that matter- freehand, so while flicking through my old trusty tome "Slaves to Darkness" I noticed something that had up until that moment eluded me. In the corner of almost every page is a round illustration of a gruesome visage.
A light bulb moment occurred, photograph the image's, resize them to fit shields, print them off & paint them.
So here's some pics of the process, more over on my blog if you interested.
Cheers.