To project their preferred identity
Humans are social beings that can hardly survive alone. People always want others to see them in a certain way in order for them to feel good about themselves. Many of the pictures people share have the goal of projecting their preferred identities to others.
To show off
All people show off but their way of showing off differs. A good looking person might show off his good looks while a happy couple might post a picture that shows off their happy relationship. Showing off is one of the powerful motivations behind sharing photos.
To send an indirect message
Many of the shared pictures have hidden and indirect messages behind them. A man who puts his pictures with his friends might be wanting to show his Ex that he has already gotten over her and that he is living a happy life.
People share photos that reflect their beliefs
People share photos & quotes that reflect their needs, beliefs and values. Once a photo provokes someone to a certain extent that person feels like sharing it.
To get a self esteem boost
Many people post photos to get likes and comments. Those likes and comments affect those people’s self esteem directly and help them feel better about themselves.
To gain social approval
A person can share a funny joke to get social approval. While most people won’t be aware of their unconscious goals their subconscious minds will usually motivate them to share stuff that can help them get social approval from friends and acquaintances.
To get more attention
All healthy humans need some attention during some points of their lives. A person can post a photo to get some attention, to remind others of his existence and to assert his presence. (See Why are some people are attention seekers?)
To satisfy a certain need
A person who feels frustrated because of the traffic jam in his city can share a photo of the crowded street to find supporters who agree with him that traffic jams are really bad.
To show what they care about
People love to show others the things that they like because those things represent them directly. A person can share a photo of a show he likes because he believes that this show represents him and that it can give others a better idea about him. (See Why do people care about looks?)
To gain recognition
A person can post a photo that shows off an achievement that he made in order to gain recognition and higher status.
Because they get rewarded
As people learned how to get social rewards such as likes, shares and comments they got more addicted to sharing certain photos. A person is very likely to share a photo if he expects to get a good social reward.
To share a moment with others
Humans are social beings. Their happy emotions increase when they share them with others. Some people share photos of certain important moments with their friends to increase their happiness levels.
Why do some Facebook friends never like your posts? Why some people never hit the LIKE button?
What does your Facebook status reveal about your personality? Why do people like to post statuses on Facebook?