Got an attention raiser during an off-the-cuff discussion on data leakage. Qua, like, not getting the first thing about what privacy has been since Warren&Brandeis’ eloquent definition, and subsequent codification in pretty hard-core, straightforward laws.
The problem being, that no theory of firm (incl public) allows subsumption of employees into slavery, of mind or otherwise. Think Universal Declaration of Human Rights, article 12. Hence, tracking and tracing every keystroke of employees, i.e., treating them as suspect of e.g., data leakage before one has any a priori clue about everyone individually actually doing anything wrong, not having been granted any rights of surveillance in this jurisdiction, is a crime in itself.
And no, the comparison with street cameras that bother no-one and make everyone safer, is a lie on two counts. And, in many countries (the civilised ones; a criterion in reverse), such (total or partial) surveillance isn’t outlawed without reason.
So, your data leakage prevention by tracing everyone is an illegal act. Don’t.
No, your security concerns are not valid. Not the slightest, compared to the means you want to deploy. Stego to files of all kinds, when all are aware of its implementation, may help much better. And supplies you with the trace you want; not to your employee that you (but no-one else) suggest is rogue – (s)he knows about the traceabilitry so will be self-censored (ugch) into compliance – but to the third party that spilled the beans. Since stego-cleansing tools may exist, your mileage may vary. Encryption then, the destruction of content accessibility for those not authorised (through holding a password/token/~), will fail when anything you send out, might have to be read off a screen; the PrtScn disabling being undone by good ol’ cameras as present in your good ol’ S8 or P900 (though this at 0:50+ is probably the typical TLA stakeout vid/result).
Conclusion: Excepting very, very rare occasions, your data leakage prevention by employee surveillance will land you in prison. Other methods, might be legal but fail. Your thoughts now on outbound traffic keyword monitoring. [Extra credit when including European ‘human in the loop’ initiatives.]