Open box, then carefully remove paper lining from box.
Using a utility knife, cut through the inside layer of the paper connecting the lid to the box. Then, pull the lid off, carefully separating the patterned paper on the outside from the lid.
Fold the patterned paper from the outside of the box toward the inside of the box. Paste it in place with the craft glue.
Decorate the inside of the box with paint, paper, etc.
Use a corner rounder to trim the edges of the photo, if desired.
Attach mounting squares to the back of the photo. (I used two on each corner for more height.)
Position photo in box, then press firmly into place.