Modern day psychometric testing
I suppose this is the equivalent of filling in "personality tests" at interviews. You know: the ones where you quickly work out what sort of person they want for the job and fill in the little boxes according to the required traits.
As it is, a lot of people (who have active FB accounts) adopt the persona of the person they'd LIKE to be - that outgoing, lively, vivacious, GSOH type that they'd describe themselves as in the lonely hearts ad - instead of the dull and uninteresting saddo who spends all his/her time glued to a screen (TV or computer) as they have no proper friends.
What an FB account, and any/all photos posted, can tell you about a person - to some extent anyway, is whether a potential interviewee harbours any of the attributes that you are not allowed to enquire about during a job interview for equality reasons. So while employers are prevented from selecting for reasons of age, gender, ethnicity it's easy for an immoral boss - or recruitment agent to preselect for interview candidates who volunteer this information in a social forum.