Have you ever noticed that some people, when their picture is taken, tilt their head to the side? The behavior is called head canting. I never knew this until I stumbled upon an article titled "Head Canting In Paintings: An Historical Study"
in the Journal of Nonverbal Behavior
Some factoids about head canting:
• Researchers speculate that it's a submissive gesture. The sociologist Erving Goffman described it as "a form of ingratiation or appeasement achieved by reducing one's overall height."
• The authors of the "Head Canting in Paintings" article examined 1498 figures in the works of 11 painters from the 14th to the 20th centuries. They concluded that, throughout history, head canting has been associated with submissiveness:
religious and mythological figures exhibited much more head canting than commissioned portraits. This finding supports the idea that head canting is strongly connected with the expression of submission, appeasement, ingratiation, and request for protection... In contrast, in paintings portraying nobles, professionals, and artists, head canting was minimal or absent.
Some googling about the subject also uncovered a bit of trivia:
Head-tilting was a signature cue of method actor James Dean. Dean's head-tilts seemed to say, as East of Eden director, Elia Kazan put it, "Pity me, I'm too sensitive for the world."