Facebook has no shortage of pictures. Facebook has no shortage of shareable pictures. From someecards to cheezburger, everybody has a "share" button. Some of these graphics are funny, some are informative, and some show you a new recipe for cheesecake. The quality and content of the shared graphics can vary wildly.
This graphic for Dream Defenders is a good example of a shareable graphic. It is attractive and has a hashtag to lead you to more information. It would be fine to add a few key points, but this graphic really gets the job done. It says who they are and gives you the option to find out more. Supporters of the cause can share it with their friends or groups, effortlessly spreading word of the cause.
This. These kinds of graphics float on and on and people keep sharing them. Not only is it poorly made (very poorly made), it's message is annoyingly vague. Who? Without whom?
When done well, a nice graphic, or even just a recognizable one, can go viral.
A very notable shared graphic is the Human Rights Campaign red equals sign. People were encouraged to make the image their profile picture to support marriage equality while the Supreme Court made decisions on the matter. People responded. Not only did they change their profile picture, they even added their own spin on it with loads of variations. It was so popular it became a meme.
Cover photos are also a valuable tool. Cover photos can show sales, they can show a business or organization in action, the possibilities are almost endless for that 851 x 315 px space.
Images get more notice than a written status. Writing that you have a sale going on isn't as eye catching as a big "50% OFF" plastered on a fan's news feed.