code: def build_pic_map(self):
          
          if self.pic_to_replace:
              # Main document
              part=self.docx.part
              self.pic_map.update(self._img_filename_to_part(part))
  
              # Header/Footer
              for relid, rel in six.iteritems(self.docx.part.rels):
                  if rel.reltype in (REL_TYPE.HEADER,REL_TYPE.FOOTER):
                      self.pic_map.update(self._img_filename_to_part(rel.target_part))
docs: Searches in docx template all the xml pictures tag and store them
          in pic_map dict