https://www.pinterest.com/marilynscreativ/create-your-own-two-tiered-wall-art/
Take a look at mlewallpapers products to understand the idea.
This is how I describe it for customers. Use a wood canvas for your background image. This image can be your hometown, a vacation spot, or any landscape. Then, publish an image that you want to feature on a wood box. This image can be a specific building, your family on vacation, or a highlight from the background image. Decide how you want to place the wood box on the background image, and place a hanger for the box on the background image appropriately. Hang the background canvas on the wall. Then, hang the box on the background canvas.