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

    hash = boostHashCombine64(hash, w);
    hash = boostHashCombine64(hash, h);
    
    for i to n:
      hash = boostHashCombine64(hash, pixels[i]);

    ret hash;
  }
}