code: def get_result(self):
          
          png = self.call()
          if png is None:
              return
          if png.startswith('GD extension must be loaded'):
              current_plugin.logger.warning('Piwik server answered on ImageGraph.get: %s', png)
              return
          return 'data:image/png;base64,{}'.format(b64encode(png))
docs: Perform the call and return the graph data
  
          :return: Encoded PNG graph data string to be inserted in a `src`
                   atribute of a HTML img tag.