new_contents: """
  Change image extensions from .png to .jpg
  
  EXAMPLE:
      >>>> echo An ![image](https://github.com/adam-p/markdown-here/raw/master/src/common/images/icon48.png) | pandoc -F png2jpg.py
  """
  
  import panflute as pf
  
  
  def action(elem, doc):
      if isinstance(elem, pf.Image):
          elem.url = elem.url.replace('.png', '.jpg')
          return elem
  
  def main(doc=None):
      return pf.run_filter(action, doc=doc)
  
  if __name__ == '__main__':
      main()
  
subject: Convert .png endings to .jpg