Cache expiration is enabled in Nginx according to the article, but cache expiration headers are showing incorrect value:
# wget -S http://example.com/image/logo.png 2>&1 | egrep "Server|Content-Type|Cache-Control|Expires"
Expires: Sun, 22 Oct 2017 13:20:46 GMT
The website is using CloudFlare.
It needed to set caching on the CloudFlare's side. Please refer to this CloudFlare article.