code: def _pngmeta(self):
          
          reserved = ('interlace', 'gamma', 'dpi', 'transparency', 'aspect')
  
          try:
              tags = self.tags
          except AttributeError:
              tags = {}
  
          # Undocumented class
          from PIL import PngImagePlugin
          meta = PngImagePlugin.PngInfo()
  
          # Copy from tags to new dict
          for k__, v__ in tags.items():
              if k__ not in reserved:
                  meta.add_text(k__, v__, 0)
  
          return meta
docs: It will return GeoImage.tags as a PNG metadata object.
  
          Inspired by:
          public domain, Nick Galbreath
          http://blog.modp.com/2007/08/python-pil-and-png-metadata-take-2.html