网页爬虫 - Python使用requests库搜到的图片src下的url是正在加载的图片

我想下载http://www.chuiyao.com/manhua/3670/393022.html里面的图片，但用下面的代码搜到的图片是这个http://www.chuiyao.com/static/skin5/images/pic_loading.gif。headers我是用的chrome浏览器network下的393022.html的Request Headers

import requests
from lxml import html

def main():

    url = "http://www.chuiyao.com/manhua/3670/393022.html"
    headers = {
        "Accept":"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
        "Accept-Encoding":"gzip, deflate, sdch",
        "Accept-Language":"zh-CN,zh;q=0.8,en;q=0.6,zh-TW;q=0.4",
        "Cache-Control":"no-cache",
        "Connection":"keep-alive",
        "Cookie":"__cfduid=d1fd7e3291dbb9fc63a4884a0441f78ee1486866309; bdshare_firstime=1486866314583; UM_distinctid=15af3096a8336d-08f956321b6c03-1d3b6853-1fa400-15af3096a84296; qtmhhis=2017-2-21-18-47-47%5E%5E%u6597%u7834%u82CD%u7A79%5E%5E%u7B2C189%u8BDD%20%u6BD2%u9B54%u6591%5E%5E1%5E%5E393022%5E%5E3670_ShG_; Hm_lvt_1317de45b1b9f5aacfe358d1694b22f9=1488746420,1490136167,1490136167,1490136753; Hm_lpvt_1317de45b1b9f5aacfe358d1694b22f9=1490136753; CNZZDATA1254167849=49322564-1486864570-https%253A%252F%252Fwww.google.com%252F%7C1490131571",
        "Host":"www.chuiyao.com",
        "Pragma":"no-cache",
        "Referer":"http://www.chuiyao.com/manhua/3670/",
        "Upgrade-Insecure-Requests":"1",
        "User-Agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36"
    }
    page = requests.get(url, headers = headers)
    tree = html.fromstring(page.content)
    print(tree.xpath('//*[@id="qTcms_pic"]/@src'))
    
if __name__ == "__main__":
    main()

为什么会这样？