WebWasher is a Personal Firewall, used to block ads. It filters, afaik, images that have the typical banner-ad size, but can also filter based on url (containing certain substrings..)

Now since rhe online advertising market is (as any market) constantly "evolving" they need a way to keep up to date (or how do you know that www.foo.com is an advertising company?)

I can well imagine that this keeping up to date is done by a fully-automated robot (or perhaps a directed one)