code: def documentCover(self):
          
          rels_pth = os.path.join(self._cache_dir, "_rels", ".rels")
          rels_xml = lxml.etree.parse(xmlFile(rels_pth, 'rb'))
          thumb_ns = ns_map["thumbnails"]
          thumb_elm_xpr = "relationships:Relationship[@Type='%s']" % thumb_ns
          rels_xpath = lxml.etree.XPath(thumb_elm_xpr, namespaces=ns_map)
          try:
              cover_path = rels_xpath(rels_xml)[0].attrib["Target"]
          except IndexError:
              return None
          cover_fp = open(self._cache_dir + os.sep + cover_path, "rb")
          cover_type = imghdr.what(None, h=cover_fp.read(32))
          cover_fp.seek(0)
          # some MS docs say the type can be JPEG which is ok,
          # or WMF, which imghdr does not recognize...
          if not cover_type:
              cover_type = cover_path.split('.')[-1]
          else:
              cover_type = cover_type.replace("jpeg", "jpg")
          return (cover_type, cover_fp)
docs: Cover page image
  
          :return: (file extension, file object) tuple.