Comment by user49598

This isn't about cryptography, this is about what data can be pulled out of bits transfered through your computer. There is no requisite that they be encrypted, they can be obfuscated, hidden, or just not recognizable as illegal to you. There is no way for you to verify that a collection of bits, put on your computer by a 3rd party, does not in fact represent something illegal. You would have to have access to every existing and theoretical encoding, encryption and obfuscation technique, and use them in every theoretical combination to verify such a thing.