The following files were taken from XBoard, modified and converted to png:
bdd40.gif  kdd40.gif  ndd40.gif  pdd40.gif  qdd40.gif  rdd40.gif
bld40.gif  kld40.gif  nld40.gif  pld40.gif  qld40.gif  rld40.gif

Read README.bitmaps for more informaion.