A cover photo is a picture that appears on the front of the photo gallery. This is the first picture people will see when they click on the Photos tab. You can only have one cover photo per gallery. The first picture posted is the cover photo. You can also select one of the other photos in that gallery to be the cover photo.
To select a cover photo, pick out the picture and then click the star that is on the right side of the picture. This photo will display on the cover of your gallery.