Bonus points if you have the site blocked under the 'file sharing' category or something like that :)

I was kinda curious, is it legal to put that picture on your website on your own?

If you're copying logo or using someone else's trademark from a real firewall page, that's a bad idea. But it can't be too hard to create a generic 'block' page that looks similar enough to real ones without using anyone else's images or logos to be convincing.

Just don't use anything federal to try and imitate.. that ends badly pretty much every time.