How could one, given a thumbnail image in ~/.cache/thumbnails, find the originally thumbnailed image?

I understand that Thunar utilizes [tumbler](https://docs.xfce.org/xfce/thunar/tumbler) to generate thumbs, and I know these thumbs exist on my system in ~/.cache/thumbnails. My goal is to write a script to check for the existence of a thumbnail on-disk for a given image or PDF. This script would be used in a workflow for quickly manipulating bulk-scanned paper documents and other images in a custom web UI. Is there a clever way to reverse-lookup the thumbnail and make a copy, so I don't need to invoke a library to re-generate for my purposes? Filenames are obscure number-strings. I'm using Thunar on Debian 10.