Use an MDM to put the device in supervisory mode. This mean you can only copy via USB to the device that put the device in supervisory mode.
See all the complaints by teachers with Supervised mode on their ipad:
https://discussions.apple.com/thread/5049820?answerId=22153837022#22153837022
The question would have been better in:
https://discussions.apple.com/community/ipad/ipad_in_the_enterprise
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MDM -- moble device management
MDMs
Airwatch, Meraki, MobileIron, Profile Manager on OS X Server, or Zenprise
For a comparison see this page:
http://www.enterpriseios.com/wiki/Comparison_MDM_Providers
Airwatch
http://www.air-watch.com/
Meraki -- A free MDM [ expect lots of email and phone calls about upgrades ]
http://www.meraki.com/products/systems-manager/
https://discussions.apple.com/thread/4067210?tstart=0
Good howto by Sergio Sosa.
https://discussions.apple.com/thread/2594001?start=15&tstart=0
MobileIron
http://www.mobileiron.com/
Profile Manager by Apple
Zenprise
http://www.zenprise.com/