Twitter Images are Blocked even when Allowing twitter.com
The firewall is configured to block the social networking category, but to allow twitter, the following URLs are configured to be allowed:
With that policy in place, twitter is allowed but images are blocked.
Twitter images are not hosted on twitter.com, they are hosted on another domain (a0.twimg.com) which is categorized as social networking. The exact URL can be confirmed by reviewing the URL Filtering logs for the host sourcing the traffic.
This is why images are blocked while the rest of the site is allowed
Add the following two URLs in the custom URL category to allow the images on twitter website: