NIST has a good solution for identifying illegal files by using hashes. They use a database called NSRL Reference Data Set (RDS). The same format is also used for files such as child abuse images.
TODO: Build support into NetworkMiner so that RDS files can be imported. Extracted files shall then be matched against the signatures in the RDS (preferably by using a Bloom filter) to see if the files might be illegal. It would also be nice to have a display filter (int the files or images tab) which allows the user to only list the files which matched an RDS-signature.