static LPair<File, Rect> gatherMarkedThingInImages(L<File> files, S thingName) {
  new LPair<File, Rect> out;
  for unnull (File f : files)
    for (Pair<Rect, S> p : loadImageFileMarkings(f))
      if (eqic(p.b, thingName))
        out.add(pair(f, p.a));
  ret out;
}