I agree this seems like a bit of overreach, but each country is allowed to make their own laws. We have a bunch of laws in Canada, and I know the US does as well, which might be thought of as a bit odd, if not downright stupid. The Lacey Act comes to mind - not all of it, but a lot of it.
This particular law would be enforceable to the extent that the person was within the reach of Namibia. No different than any other law. Given how much I enjoyed hunting there, and how much I'd like to again, I'd likely comply.
Is this law a good idea? Well, given that it won't stop the posting of most pictures, it probably won't make much difference to anyone's views of hunting, whether in Namibia or anywhere else. But if Namibia wants to make a statement, well, that's up to them.
Personally, AH is the only social media platform where I've ever posted my pictures, Some have ended up on social media because outfitters (without my approval) posted pictures of me with trophies.
Would I still hunt if I couldn't post my pictures? Absolutely. I take pictures principally for me, and for friends. I have no need to show them to others, although I've been happy to do so here.
I think we need to maintain a sense of balance and proportion here. The world is changing, and not for the better. I am hunting in September and part of the deal is that I will not publish any pictures anywhere, nor will I make it known where I have hunted what I'm hunting. Sound a bit much? The place I'm hunting wants no bad publicity, because it could seriously impact what they do. I can't argue with them; in fact, I think they're right. But it's a great deal for me, and I'm happy to agree to the conditions.
How important is bragging to hunting anyway? You can still take and share pictures with others, just not on social media.
This strikes me as no big deal. Let's get behind the good guys and save our anger for the bad guys. Namibia is one of the good guys.