>Admittedly I don't have any data for this, but I think it's fair to assume that this number of 600 would go down to 10-20 or so after a quick human review of the data.

Yes, you have no data for this. Sieving out 95% of hits just because a human glanced at the results is a ridiculously optimistic estimate, even if you manage to staff the screens with humans who are actually good with strange faces; and most humans are not. Humans on average not being good with faces (of strangers) is why witness statements are so unreliable and put so many innocent people in prison (and we have data for that). And you want to sieve out faces that the computer already thought were similar enough to warrant a match, which won't make it any easier.

They're trying to sell a horrible system that does not work correctly to the public. It doesn't matter if the public thinks it is worth it after they massively misrepresented what it actually can do. (Oh, and the German public isn't exactly known for been keen on surveillance either).

>I wouldn't call that a failure.

I would and I do.

>If the German police could have fed his photo to this system that would have been extremely helpful, even if it would have meant a couple hundred officers having to review photos for a day.

This is not backed by any data either. He could have easily been one of the 1/3 of people the system fails to detect. Or he could have further disguised himself for the system not to trigger. Oh wait, he did[1], with a beanie and a scarf and later with hood. And nobody took notice, because a lot of people looked like that as it was cold outside. In the summer, you'd just get some big ass sunglasses to cover enough of your face that the already poor system would not have triggered.

And by the time the police actually had a preliminary ID and a preliminary picture of a sufficient quality that would have allowed facial recognition, he already had left Germany. And by the time they actually had fingerprint evidence he even was in the truck, he had traveled 3 or 4 countries.

The likelihood that such a system would have helped finding Amri, even tho he actually took trains and didn't just go into hiding close by or took a car, is minuscule. Those "couple hundred officers" would most probably had more success if they spent their time actually investigating Amri and his acquaintances[2]. Also, let's not forget that by the time we would have used the facial recognition system, he had already murdered the truck driver and carried out his attack murdering another 11 people, injuring another 55.

So in the end, even your terrorist-strawman here is pretty bad at justifying such a system.

[1]
https://www.spiegel.de/politik/ausland/bild-1128683-1091474....
https://www.spiegel.de/politik/ausland/bild-1128683-1089847....

[2]
Well, maybe... Given the massive failure by law enforcement before the attack, I am actually not too sure. Amri had been under surveillance for months before the attack, and they even had a snitch close to him, who even drove him from NRW to Berlin. He had previously been convicted in Tunesia (in his absence because he had already fled to Italy) of robbery, and was further investigated for theft and drugs, and in Italy he was convicted of arson and battery, and spent more than three years in jail, where he started a lot of fights and was already being tracked by Italian counter-terrorism because he showed lots of signs of radicalization. He was under surveillance in Germany by counter-terrorism as well, but they further found out that besides violating the movement restrictions of his asylum, and using multiple identities (they knew about 3 or 4 before the attack, but in the aftermath they found he was using up to 14), and his links to radical Islamist groups, he also paid his bill by dealing drugs. He also was known to the US agencies and had been put on the US No Fly list. His asylum had been denied, which prompted him to try to go to Switzerland with fake documents (to marry somebody there and avoid deportation), but he was caught and jailed, but then let go again because his replacement papers from Tunesia were expected to take more than 3 months to arrive. Let go even tho he was known to be a flight risk, a violent convicted criminal, a drug dealer and very chummy with radicals, and even tho he could be jailed for more than 3 months for being a deportee alone awaiting deportation.

This guy was a walking red flag, and German law enforcement had enough evidence to put him into a prison cell for the drug dealing alone, and he had a deportation order, but they decided not to act.