srecord noeq HashBWImage(BWImage img) {
  long hash;
  
  long get() {
    if (img == null) ret hash;
    
    int w = img.getWidth(), h = img.getHeight();
    int n = w*h;
    byte[] pixels = img.pixels;

    addToHash(w);
    addToHash(h);
    
    for i to n:
      addToHash(0xFF000000 | rgbIntFromGrayscale(ubyteToInt(pixels[i])));

    ret hash;
  }
  
  void addToHash(long x) {
    hash = boostHashCombine64(hash, x);
    printVars ifdef HashBWImage_debug(x := longToHex(x), +hash);
  }
}

Began life as a copy of #1034798