It seems unlikely but there is a lot of research that illustrates that most people can assess someone’s personality based on very little information. A photograph, an office, bedroom, a personal website have all shown to be sufficient to achieve a better than random result in guessing personality as well as sexual orientation.
A German study on this (Borkenau 2009) found that just seeing a headshot of someone for 50 milliseconds was enough to assess extraversion. In order to find out how the participants were able to spot this trait, Borkenau and his colleagues had a second group look for visual characteristics in the headshots. It turns out the people who were rated as extraverted looked more cheerful and smiled more than others. This makes sense since a lot of research has found that extraverts actually are more cheerful than introverts.
While spotting extraversion by looking at a picture for 50 milliseconds may sound impressive, it’s probably not. Thing is, the study looked at all the five traits included in the popular Big Five model of personality – Extraversion, Neuroticism, Agreeability, Openness to Experience, and Conscientiousness. And the participants only got one right. So why did they get any right at all?
The answer may be found in how they got the others wrong. It turns out that the people with headshots showing cheerful and smiley faces were all considered to be extraverted, low on neuroticism, and high on agreeableness. These traits are all socially desirable. In other words, they attributed socially desirable traits to people who looked cheerful. And as it happens, extraverts generally report feeling happier than introverts so they probably smiled more – but that appears to have been just a happy accident.
This study suggest that people make judgments based largely on wishful thinking. They see a person who is smiling and they assume that he or she is what they consider a pleasant person. Social psychologists have shown this phenomenon numerous times; people look at conspicuous information, like a broad smile and ignore the less obvious information, like that the person in question is being photographed so he may be smiling even if he isn’t that cheerful or he may not be smiling because something caught his eye.
They way to assess someone’s personality is not by “speed reading”, it’s by long-term observation. To look at how people behave when you are familiar with the situation, to gather lots of data and see patterns emerge. If you thinks someone is pleasant because they smile it only means you’re an easy target for sales people.