Do you mean the ?####_fullhd.png (might be without the 'hd')?
This would be such as e0112_full.png for one of Sapphira A's cards.
If yes, all you need to do is open the details of each and every desired card (owned or not). The app will download this file and the nude or lock image.
If you have already done this with all cards you own, or with a certain selection of cards, then there is nothing more to download.
The app will have downloaded these photos as each card's details were viewed.
Now, just go to your computer and find the data folder, then you can find the individual file within any card folder.
However, this is not an easy route.
You may want to have all of these grouped together in one location.
If that is the case, then go to your computer and find the data folder. Then, input "_full.png" in the search field. No need to add the hd unless your computer handles search differently than mine.
You will find the search results for every card that has a full image.
Then, select all search results, and click Ctrl-C to copy all them. Then, simply paste that in some other folder.
(copy, not cut)