Some software like digital image processing tools work with sidecar files which are placed next to the original file. E.g. darktable uses .xmp as file extension, rawtherapee .pp3.
When you sort out / delete original files outside of the software, you end up with orphaned sidecar files.
find_orphaned_sidecar_files.py helps in such a situation by finds such duplicates.
Example usage:
$ find_orphaned_sidecar_files.py pics pics/dir1/orphaned1.xmp pics/dir2/orphaned2.xmp