There is a shadow box in the centre of the frame, and its height was not as tall as the 11 x 17 poster I had originally printed, so I had to go into photoshop and remove some of the top and bottom of the poster to make it fit.
It took way longer than I had thought to open the frame, as it was never meant to be taken apart. It was nailed and glued together very tightly. After pulling it apart, I was able to remove the flower picture and add a sheet of black construction paper to the back of the shadow box and then affix the newly printed Mandrake poster, before putting the whole thing back together.
I think the final result is pretty awesome, don't you! I can't wait to find a spot to hang this gem on my study wall - that's the fancy name I'm giving my living room.