>> There's also a possible end game where the child porn traders [...]
> Once again, this behavior would get Hungary booted pretty quickly.
I'm sorry; I should have made myself clearer. In that paragraph, I've taken an aside and moved from Hungary (or any other government) as the adversary to child-porn-sharers-in-general as the adversary, and also changed the adversary goal.
No matter what you do, you can't "boot" the child porn sharers, because they're the ones who actually define what images you're legitimately trying to block.
> Also it is important to remember these are hashes. Not all images of the US flag would trigger the system only that specific image that has a hash collision.
They're approximate perceptual hashes, designed to come up with close values on close pictures. The US flag has an officially defined appearance. You'll get the same hash for any two close-cropped, straight-on images of the flag, the kind you might embed in your Web site. They'll be at least as close as two reprocessed versions of the same child porn image.
I was oversimplifying, though. You're not going to be able to tweak just any child porn image to make it hash like just any flag, unless you're willing to distort it into unrecognizability. And flags and logos might be bad candidates in general, because they're going to give DCT output that's wildly different than what you'll get from most photos. But if you had a relatively large library of child porn and a relatively large library of heavily-used effectively unbannable images of whatever kind, you should be able to find a lot of the child porn images that you can tweak to hash like one or another of the heavily used ones.
... and if you're generating fake child porn from scratch using ML, you can probably hack your ML model to bake the hash of one or another unbannable image into everything it creates. You could probably make those matches pretty damned close.
So, once they got the whole thing down, they should be able to force the system to greatly tighten its match thresholds and/or deal with a really high false positive rate. In fact, they could probably make things bad enough that they could end up with a pretty large collection of child porn that the operators would be forced to completely exclude from detection.
Now back on the original authoritarian threat model:
> I just think this in a complicated and ineffectual bullet that can only be fired once because it has a fingerprint of the person who fired it.
For the "authoritarian" purpose, you may be right... although I wouldn't be surprised if it stayed under the radar for longer than you think. If the image you want to suppress only circulates among your own people, and if you're the authority who receives and verifies the reports on your own people, then all you have to do is to keep the overall volume down enough that it doesn't make anybody suspicious enough to demand that you show them the reports you're getting.
If you're a relatively small country, the number of people who share some local meme you care about may be quite a bit smaller than the number of people who share some new real child porn image.