code: def source_filename(self, docname: str, srcdir: str):
          
  
          docpath = Path(srcdir, docname)
          parent = docpath.parent
          imgpath = parent.joinpath(self.filename)
  
          # Does this exist?
          if not imgpath.exists():
              msg = f'Image does not exist at "{imgpath}"'
              raise SphinxError(msg)
  
          return imgpath
docs: Get the full filename to referenced image