If your book is a low content book, only the front cover will show up for customers to see and you will have to add A Plus to show off the back cover and interior pages.
In general, a low-content book has minimal or no content on the interior pages. These pages are generally repetitive and designed to be filled in by the user. (From Amazon's KDP's definition of low-content books).
However; there is still a way to accomplish showing photo's, but will require a little work by you.
Click here for our article on adding A+ content to your Amazon KDP Listing.