Recently I've been helping out a customer with perhaps the strictest URL filtering policy I have seen in a while!
URL categorisation is in place and large sections of the internet such as "blogs / personal pages" & "social networking" were being blocked. What makes this unusual is that Google images is a popular tool, the mix of these two made it "appear" that Google images was broken.
Broken you ask? Yes, basically if you search for something harmless like "HP Laptop" or "Nokia Phone" some of the results are actually stored on personal pages (forbidden categories) , as the image is blocked your browser returns a broken image icon which makes it look like the page loading failed!
With the help of a very helpful Blue Coat guy I have a solution.
To start with you'll need an image to insert into the page, something that shows the image was blocked, this open clip art denied sign worked nicely for me. Next you'll need an Intranet web server to save the image on - IIS or Apache will do the trick, it doesn't matter where the image is as long as your users can "see" it.
In the VPM you'll need an object representing all your blocked categories and a to create a new rule..
Source = Any (or internal users, whatever)
Destination = Combined object (Call it something like Blocked_Images), in the top box you want your category object, in the bottom box you want a "HTTP Mime Types" object which matches all images - Screen Shot 1 should help.
Action = Combined object (Named something like Return_Blocked_Image), in the top box you want two actions a "Return Redirect Object" which redirects to your Image and then "Allow" which permits the HTTP request to your image. - Screen shot 2 should help
Install the policy and job done! I think you'll find this is a very neat solution!