The backgrounds come with the file if you download it from 3dcuts. They are not included with the Silhouette SIL online store download. They are in jpg format. The top and bottom one are photographs from our trip to Iceland. The middle one I created using Illustrator. Love that gradient tool!
I have made the file available for purchase to other crafters on my sales website - 3dcuts.com
The cutting file is available here:
And you can view the assembly tutorial here:
Check out my entire collection of shadow boxes here: http://3dcuts.com/shadow-boxes-nature-themes/
Which background do you like best?