If you have a landscape photo, the sides may get cut off if being used a full page photo or cover photo. To adjust for this, you need to add a border to the top and bottom or resize the photo so there is a border all the way around it.
To do this, create a 300 dpi 8" X 10" (for covers), or 7.75" X 9.75" (for photo pages or section dividers), canvas in a third party photo editing program. Create a background of a color of your choosing. Once you have chosen a color, Import or Place your photo over the background and size it so that the entire photo is visible. You can go as far as adding your own text if you want.
When you're done, save the image as a jpeg and import it into the designer. If you added your own title, make sure the Background color in the display options is set to transparent.