Cut the backer board to size, as well as the scrap wood pieces to exactly fit the board. Arrange to make sure the pieces fit.
Print out graphics to fit each piece of scrap wood. My graphics are just old postcards, maps and even a quick internet download of the poster from my favorite movie. Trim to fit. Decoupage the graphics onto the wood blocks, one by one. Add Mod Podge to the wood, smooth down the paper on top, and let dry for 15 - 20 minutes. Then apply a top coat and let dry. Repeat and let dry completely.
Distress edges of the blocks with a sander, gently.
Reassemble the design on the backer board. Leave flat or place wood pieces as risers under some pieces for interest.
Use wood glue to attach all pieces, including the risers, to the backer. Let dry overnight.
For the frame, I decided that I wanted a basic, rustic look. You will create simple butt joints. Grab the square dowel rods and mark where the pilot holes should go at the end of each piece.
Drill the pilot holes (these will prevent the dowel from splitting while screwing. Then attach the dowel pieces to the frame using the wood screws.
Paint the frame with white paint and let dry before hanging or displaying.