When using Web Filter to block categories, and also using the Pass Sites list to pass some websites, these passed websites may load without graphics. That is because these sites are loading graphics from another domain but without using a referrer. This graphics site, however, will usually categorize in the same category as the site which it contains graphics for. In most cases, this is never a problem as most sites will use referrers. On the Web Filter app under the "Advanced" tab, you can see an option for "Pass if referrer matches any Pass Site". However, when sites do not use referrers, problems can arise.
A good example of this is Pinterest. Pinterest.com categorizes as Social Networking and you can pass it at the "Pass Sites" tab, even when blocking the Social Networking category. However, pinterest.com loads images from pinimg.com. This site also categorizes as Social Networking and since it is accessed without a referrer, will be blocked by the category block for Social Networking. The only resolution to this problem is to create a Pass Site entry for pinimg.com.
You can see this traffic in Reports at Reports > Web Filter > All Web Events. Look for the session to the site you loaded without graphics and look for other sites associated with the session that are blocked by a category block. Pass this blocked site to have graphics load properly.Follow