Sometimes, the banner photo will need its height adjusted. Really tall photos take up a lot of screen real estate, so it's often best to reduce the height of tall photos.
To adjust the height of a photo, find the bottom of the photo, where it meets the start of the body of the page, and place your mouse cursor over this meeting line. The cursor will turn into a double headed arrow. Click and drag up or down to make the image taller/shorter.
If all the image is showing, you won't be able to make the image taller. Subsequently, there is a minimum height (300 pixels at 1200 pixels wide) for the banner image, so you won't be able to make the image shorter if it is already at this height.