A cover is the larger photo at the top of your timeline, right above your profile picture. Note: Like your profile picture, cover images are public, which means anyone visiting your timeline will be able to see them.
Facebook found that people have a better experience viewing your timeline when they see a cover that is as unique and individualized as you are. This helps people learn more about you. It also helps us prevent spam, fake profiles, and other content that can detract from your experience on Facebook. An easy way to ensure your cover image is unique is to choose an image from your life, like a photo from a wedding, day at the beach, or birthday party. If you want to use a photo to show solidarity or express support for a cause or organisation, you can still post a status or a photo and feature it on your timeline.