Comment by zepto | Hacker News Reader

Comment by zepto | Hacker News Reader

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No, what you have said is bullshit. The perceptual hashes are not generalized. They do not match ‘child porn’ or ‘pride flag’. They match specific photos from a database.

You might argue that that database could contain a specific photo of a pride flag. You would be right, but there are safeguards against that. The system will not trigger with just one match. A set of multiple images must match. So no, the system won’t match a pride flag, and no the system won’t match a specific picture of a pride flag.

The next argument would be that a whole load of pictures of pride flags could be uploaded and then someone who has enough of those pictures would trigger a match.

This is true from a technical standpoint, but there are two more safeguards. The database is maintained by NCMEC, which is a non profit dedicated to tackling child abuse, and matches are visually confirmed by Apple.

So, to match someone who just happens to have a pride flag in a picture is not possible. To match someone who has a set of specific pictures of pride flags is only possible if both Apple and NCMEC collude.

So no - it can’t target a pride flag at all, much less as easily as CP.

>A set of multiple images must match.

How many exactly? The threshold is secret, it could be 1 or 2 or maybe it is dynamic and depends on stuff like your identity.

It could be 1 or 2, but the claim is that it is set to only detect people who are actually building a collection of CSAM images because Apple doesn’t want this system to flag people who are unlikely to be actual criminals. I.e. they don’t just want no false positives, they don’t want positives that aren’t highly likely to be criminal. I’m guessing it’s a lot more than 2.

> but the claim is that it is set to only detect people who are actually building a collection of CSAM

From what I read the threshold is for a different purpose, ,the false positives are too many so to reduce the number of reports the threshold workaround is introduced, so is a hack to workaround the false positives and not a threshold to catch people with big collections.

I have seen both in comments from Apple. Certainly spokespeople have talked about wanting any reports to NCMEC to be actionable.

I think a lot hinges on what you call a ‘false positive’. It could mean ‘an image that is not CSAM’ or it could mean ‘an account that has some apparent CSAM, but not enough to be evidence of anything’.

I think it is clear that Apple will have no choice, if they for sure find 1 CSAM image they can't say "it is just 1 img so it is not a big collection..." they have to send it to whoever to handle it.

What would help me with this kind of things would be more transparency, like to know the algorithm, the threshold, the real numbers of false positives, can the hashes be set per country or individual, can independent people look inside iOS and confirm that the code works as described...

What would also help is to know for sure hoe many children were saved by this kind of system,

> I think it is clear that Apple will have no choice, if they for sure find 1 CSAM image they can't say "it is just 1 img so it is not a big collection..." they have to send it to whoever to handle it.

This is a misunderstanding of how it works. The threshold has to be met before a detection occurs. Unless the threshold is met Apple doesn’t get to know about any images.

As for independent auditing and transparent statistics, I fully agree.

You misunderstand my comment, maybe is my fault.

Let's say the threshold is 10 , you trigger the threshold so Apple checks all the 10 images , but 9 are false possitive and one appears to be a correct match, Apple will report you for 1 image ... so my point is that is not designed to catch people with big collections of CP, is designed to not trigger to often.

Ok, but the threshold is 30. It seems unlikely to be a problem.

Yeah, I was commenting about the "collection" part of the comment.

"(...) but there are safeguards against that."

Hah! Nice one :D

Apple have described the safeguards. If you want to claim they are lying, by all means do so.

This is pure speculation.

Not one line of it is speculation. This is taken from Apple’s public docs.

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