You can also check out the H!P Wikia:
http://helloproject.wikia.com/wiki/Kobushi_FactoryLots of pictures there clearly showing off their faces, especially on the individual member pages.
(dammit, I was whipping up my own guide but shirenu beat me to it ) On second thought, I'll post my quick guide anyway:
Ayapan: the leader, kinda chubby, small eyes, big boobs
Rio: short height, short hair, kinda big nose
Minami: prominent jawline
Rena: big eyes, mole under chin, kinda looks older than her age
Hamachan: relatively tall, wide baby-ish face, probably the most well-known of the bunch
Taguchi: the other short one, small head, bob haircut, very expressive face
Sako: the other tall one, round button nose,
kinda looks like JunjunRei: innocent smile, really long hair and neck
Also some music videos have them decked out in their member colors:
And there's the
Greeting series of videos that each focus on a few members at a time: