code: public void setCustomLayer(final BufferedImage CUSTOM_LAYER) {
          if (CUSTOM_LAYER == null) {
              model.setCustomLayerVisible(false);
              return;
          }
  
          model.setCustomLayer(CUSTOM_LAYER);
  
          if (model.isCustomLayerVisible()) {
              reInitialize();
          }
      }
docs: Sets the buffered image that represents the custom layer.
  It will automaticaly scale the given image to the bounds.
  The custom layer (which is a buffered image) will be
  drawn on the background of the gauge and could be used
  to display logos or icons.
  @param CUSTOM_LAYER