Once you press OK to accept the changes, right click and copy this new image and past it in your book/box photo.
Repeat these procedures of copying and pasting until you get the result you desire. Add more photos on your cover until you are satisfied with the look.
If you’re doing a box, you’ll want to skip this step.The next step is to change the back cover color. This is not necessary so you don’t have to, but some find it helps with the look. The choice is yours.