A fun open access paper about personality judgments based on seeing just a picture of someone. One of the authors is Samuel Gosling, whose work lies behind the online Big 5 personality test I recommend to the curious. You can learn a lot just by looking at someone, and in this paper they break down how different things strike observers. Hairstyle, manner of dress, posture, expression, there are many visual cues that tell us something about personality.
There are a number of other studies referenced in the paper that demonstrate the additive value of seeing someone in person or on video. There are many other cues that are dynamic, and thus harder to see in a picture. However, you don't need much time to form pretty accurate judgments in this fashion, although unsurprisingly the accuracy goes up with more exposure.