WeChat.ServerMessage.XmlMessage.reply_image

You're seeing just the function reply_image, go back to WeChat.ServerMessage.XmlMessage module for more information.
Link to this function

reply_image(to_openid, from_wx_no, timestamp, media_id)

回复图片消息 - 官方文档

<xml>
  <ToUserName><![CDATA[toUser]]></ToUserName>
  <FromUserName><![CDATA[fromUser]]></FromUserName>
  <CreateTime>12345678</CreateTime>
  <MsgType>image</MsgType>
  <Image>
    <MediaId><![CDATA[media_id]]></MediaId>
  </Image>
</xml>