I haven’t done it myself, but this is what I guess. So, I apologize if it doesn’t work.
There are three layers:
Bottom layer: Photo
Middle layer: Text
Top layer: Same photo with background removed effect
Check out these threads:
Solved: What are PhotoPop cards? - Zazzle
PhotoPop typography? - Zazzle
PhotoPop revisited - Zazzle
PhotoPop for designers - Zazzle
PhotoPop for all designers, please! - Zazzle
Not sure to understand clearly your point, if it’s about the back and front pics that the customer changes with its own:
When you create the design, you choose a picture, define it as a template, then you add your text ( above it ) and you copy paste your first picture, which is then seen as a second occurrence of the same template and not a new picture.
You remove the background from this second occurrence, and then when your customer will change the picture, it will simultaneously replace both of them. But the customer will have to remove the background from the top layer picture by himself, because it’s not possible for us , designers to define it to be automatically applied.
Thank you 
These links are very helpful - thank you!
from reading many post that you need to be granted PhotoPop from Zazzle. I can make it look like the photo pops but I was looking to do that automatically without customer having to remove the background. Thank you
Impossible for now, we all hope it will be in the future !
Yes, I hope so!!