how can I recover my wallpaper from an old backup?

I had some problems with my iphone 12 max pro recently stuck on 14.6. I used the itunes restore functionality and decided to start fresh and not restore from my local MacOS BigSur backup. The restore method upgraded me to 14.7.1, so I cannot restore my 14.6 backup - but I have the backup and purchased imazing a while back. Can anyone provide instructions on how to find and extract the wallpaper image I had from a vacation in the past? It was a picture I took - not something searchable on the web and I have gone through my hundreds of thousands of pictures from all my iPhones back to my original iphone, and cannot find the darn file. I know it's trapped in the backup - I just cannot find a way to extract the file...