Facebook may ask you to upload a picture of your face to unlock a temporarily suspended account
According to Facebook, the photo request is designed to find suspicious activity at certain points in the use of the app including the opening of an account, and when making a friend request. The demand for a photo is sent automatically, and Facebook looks to see if the photograph is "unique" among other tests, to determine if the account being temporarily suspended is legitimate. Photos are looked at manually and through automated methods.
What might set off bells and whistles is an account where all previous postings come from New York and all of a sudden, the posts are coming from another country altogether, say Russia. The photo requests started earlier this year, and when you get one it is accompanied by the following written comment: "You Can’t Log In Right Now. We’ll get in touch with you after we’ve reviewed your photo. You’ll now be logged out of Facebook as a security precaution."
If you suspect that someone is messing with your Facebook account, go to Facebook.com/hacked.