I have a speculative (read: probably garbage) theory, orthogonal to the one in this article, that you can get some idea of a person's personality from their looks. My hypothesis is that as long as you are not too young, then the most common expressions that your face assumes - frowning, smiling, scowling etc - have some effect on your wrinkles and facial muscle development. So maybe by looking at someone, you can see some aspect of the history of their facial expressions and hence guess if they are generally a cheerful, miserable or sneering kind of person.
A corollary (also probably garbage!) is that one of the clues that helps you guess a person's nationality by looking at them is these similar aspects of 'face-shaping': either through the most common sounds they make while speaking their language, or the typical mannerisms of that culture. Obviously this would only work within a group of people that have broadly similar racial characteristics. My 'sample group' is mainly from western European countries.
Hey Bill - interesting point, I've wondered along those lines myself. Also if I may - why not kill the "probably garbage" part when commenting? Just say what you think mate, it's a really well-reasoned theory and the discussion's better for it.
You don't even have to assume that past expressions permanently effect facial contour (though that's probably true). Whenever a person is being evaluated -- and taking a mugshot for a study certainly counts -- they adopt a pose/expression. They are almost certainly sending a message about themselves with their choice of expression, and that choice is biased by what's worked in that person's past interactions with others. Unless they're deeply dishonest, they'll send a generally-true message about their personality.
You could start to test this by seeing if the accuracy of third-party estimations holds up when people evaluate photos of sleeping/anesthesized faces.
On the other hand, a bleaker interpretation is also possible. Maybe you are born with a certain kind of face, and will always be judged that way no matter how you behave. So over time, only by playing-to-type do you get positive feedback, and the facial stereotype becomes destiny.
My untested hypothesis is that your parents and peers expect you to act a certain way (based on your appearance) and many people accept these subtle nudges without resistance. So, it basically becomes a self-fulfilling prophecy.
I don't think there's hard evidence of it though - just one's own experiences.
I can guess the P/J split (J types have a serious look) and the F/T split (F types usually indicate to you their mood with their expressions) with a quick glance at the face, but haven't done anything in a controlled setting.
A corollary (also probably garbage!) is that one of the clues that helps you guess a person's nationality by looking at them is these similar aspects of 'face-shaping': either through the most common sounds they make while speaking their language, or the typical mannerisms of that culture. Obviously this would only work within a group of people that have broadly similar racial characteristics. My 'sample group' is mainly from western European countries.