I don't know of any directive, but the military itself has been copying its own ID cards for decades.
![Confused :???:](./images/smilies/icon_confused.gif)
For instance, if you want to pick up your spouse's prescriptions at the Brooke Army Medical Center pharmacy, they will tell you to either bring the spouse's ID card -- or a copy of the front and back. Policy of the commanding officer (and every other military pharmacy I have ever been to). Keep cop of my wife's in my wallet.
Me, I'd send in a copy and not worry about it. I am sure that's what I did if they asked me for one when I first got my CHL while on active duty (but I don't recall that it was necessary then). AFAIK, the feds have not issued any warrants on me for doing so.
![Mr. Green :mrgreen:](./images/smilies/icon_mrgreen.gif)