No software in the world will be able to tell a legal mp3 or picture from an illegal one. That would be possible only by enforcing DRM (Digital Rights Management) for _all_ files, which is quite against the Open Source spirit.

And the solution definitely can't be to forbid _all_ mp3s and pictures in a school setting - that wouldn't be freedom (of mind) at all.

So imho the key is in education - education about what is acceptable and what not. And manual checks.

Greetings,
probono