So you lock down PrtScrn via GPO, easy and not reversible (make it a user GPO and it will apply at logon). having said that, Windows 7 onwards has the snipping app (unless you use applocker or EMET, which you probably won't), it appears you are going to have to invoke, as a minimum, the following:
Disable clipboard / prtscreen via GPO
Disable the Snipping Tool app via AppLocker or EMET
Create a DLP that picks up attachments and forces them through an Admin workflow before they are released by the email server (O365 can do this very easily)
Disable USB access
But, and trust me on this, unless you are working for the gov at Official Sens or higher, there is no data that any company can be that sensitive about.
Disable clipboard / prtscreen via GPO
Disable the Snipping Tool app via AppLocker or EMET
Create a DLP that picks up attachments and forces them through an Admin workflow before they are released by the email server (O365 can do this very easily)
Disable USB access
But, and trust me on this, unless you are working for the gov at Official Sens or higher, there is no data that any company can be that sensitive about.