I don't know how other people do it
but I have a probably-not-unique voting system:

baby/children in picture: +1
Slightly funny looking but literate: -1 for looks but +1 for literacy = average vote
Exceptionally good looking but obvious fuckwit: -2
Gun in picture: -3
Pleasant but not exceptional: 5 (ie a vote of 5)
Can't see eyes (sunglasses or looking away): 1 (ie a vote of 1 - fuck you, why should I rate your looks when I can't see them?)
(Emily Bruce-Dickinson http://jovialfellow.blogspot.com/, Sun 16 Sep 2007, 12:16, archived)

Sounds like a good system.
You can only judge the literacy or fuckwittery of those with Meet Me profiles though, which makes that one more difficult to be consistent with.
( nick the greek, Sun 16 Sep 2007, 12:24, archived)