Banner download robot

For controlling purposes I want a robot written that downloads all ad-banners from several of my websites. So your task would be to analyze the structure of the website/URLs and write a robot that detects and downloads all banners automatically and saves them i a database for further usage. A very good and detailed technical and non-technical documentation is required that allows i.e. interns to understand from which site and where exactly a banner-ad was from.? The robot also needs to be able to work in "log-in only" areas (community) and check for rotating banner ads (i.e. several banner are shown on one site).