A long-time client has asked us to help screen their work machines for pornography. They're worried about liability if sensitive materials were found. Their main concerns (for obvious reasons) are video, audio, and image files. If possible, they'd also like to scan text-based documents for inappropriate content. They have a hierarchy of not-for-work content starting with blatantly illegal (I don't have to list details), moving down to obviously offensive, and also including things that may be offensive to some - think lingerie ads, joke cards featuring butt cracks, and anything related to Howie Mandel.

My questions are:

• Is this ethical? I think it is since every employee legally agrees that their work machine belongs to the company and is subject to search. The screenings are not to occur on personal machines brought to work.
• Is it feasible? I've done a lot of image processing/indexing but this seems like a whole new world of complexity.
• Any references to successful techniques for discovering porn?
• Is it appropriate for me to archive the results when something is discovered?