I can think of many reasons for this, but what's been on my mind lately is the picture issue. I've heard so many people say that someone doesn't look the same in real life as they do in their pictures, and often, that they looked better in their pictures. For the longest time I just figured that people chose attractive pictures for their profile, and maybe in real life they don't normally dress as nicely or wear so much makeup. But as I was uploading some new pictures, I realized that there is more to it than that. Even if you don't purposely try to look attractive in your profile pictures, the pictures that you take are already selective, only showing certain parts of your life. When I look through my pictures, I see special occasions: trips, dance shows, parties, beach days... all kinds of fun things that are far from what I do every day. I consider myself an introvert and I like to spend most of my time alone, so the pictures taken at social events do not reflect the majority of my real life. When you think of it that way, it's weird that we would expect people to look the same in their everyday lives as they did on those special occasions.
I mostly just take pictures when I'm traveling, and I have one close friend at home who takes a lot of pictures. So my profile is mostly travel pictures and pictures of fun times I've shared with that friend. But I don't have a lot of pictures of myself at college. If I had met college friends online first, they would have been in for a shock when we met in real life because none of the pictures they saw would have shown me in that environment, so their impression of me might be very different from who I was at college.
I was psyched last year when a student took tons of pictures from our dance show. Not only were the pictures really nice, but I finally had some pictures where I wasn't happy or psyched. My dance was serious, and even though I was acting, in a way I wasn't because the dance meant something real to me. Since all the anguished poses and expressions were clearly part of a show, it was okay to post them. Because let's face it, it's not socially acceptable to post candid pictures in which you're really unhappy. We don't take pictures on those occasions. I like my profile to match the way I feel, so I've often used icons to express negative feelings since I didn't have any pictures that matched my current emotions. The dance pictures did help a lot, though.
I guess the bottom line is that, while you can learn a lot from a picture, it is important to keep the context in mind and realize that it does not necessarily reflect the person's everyday life. Many parts of our lives are just not socially acceptable to capture and share.