I do not have a strong personal presence on the Internet. I do not have a Facebook account, a Twitter account, and even on OCC, I do not have a profile picture, all because I do not want to or do not care to have one. If you do though, you should try to be conscious of what it says about you in more ways than just what you post. Researchers at the University of Missouri, Columbia have found that specific aspects of one's profile picture on Facebook can set an impression for anyone looking at it, including potential employers.
Profile pictures have the power to affect the perceived attractiveness of a person, socially, physically, and professionally both positively and negatively. Simple headshot pictures with negative comments make someone appear less attractive, but a picture with social cues and positive comments makes the person appear more attractive. These social cues are just things that provide information about the person, such as an image of them playing a sport, or for overclockers, building a computer. They show that the person is active and interested in something.
What this research shows is that if you want to make the best impression with your profile picture, make sure it shows who you are, and not just what you look like. Also you want to be aware of what others are saying about you, as these comments affect what others think of you.