static L<RectAndMD5> segmentScreenToCacheFile() {
  new L<RectAndMD5> out;
  BWImage bwScreenShot = shootScreenBW();
  for (Rect r : autoSegment(bwScreenShot))
    out.add(RectAndMD5(r, rgbMD5(bwScreenShot.clip(r).toRGB())));
  saveTextFile(segmentedScreenCacheFile(), struct(out));
  ret out;
}