<story><title>The deceptive PR behind Apple’s “expanded protections for children”</title><url>https://piotr.is/2021/08/12/apple-csam/</url></story><parent_chain><item><author>stickfigure</author><text>The false positive rate for any given image is not 1 in a trillion. Perceptual hashing just does not work like that. It also suffers from the birthday paradox problem - as the database expands, and the total number of pictures expands, collisions become more likely.&lt;p&gt;The parent poster does make the mistake of assuming that other pictures of kids will likely cause false positives. Anything could trigger a false positive - especially flesh tones. Like, say, the naughty pictures you&amp;#x27;ve been taking of your (consenting) adult partner. I&amp;#x27;m sure Apple&amp;#x27;s outsourced low-wage-country verification team will enjoy those.</text></item><item><author>fortenforge</author><text>Lots of people responding to this seem to not understand how perceptual hashing &amp;#x2F; PhotoDNA works. It&amp;#x27;s true that they&amp;#x27;re not cryptographic hashes, but the false positive rate is vanishingly small. Apple claims it&amp;#x27;s 1 in a trillion [1], but suppose that you don&amp;#x27;t believe them. Google and Facebook and Microsoft are all using PhotoDNA (or equivalent perceptual hashing schemes) right now. Have you heard of some massive issue with false positives?&lt;p&gt;The fact of the matter is that unless you possess a photo that exists in the NCMEC database, your photos simply will not be flagged to Apple. Photos of your own kids won&amp;#x27;t trigger it, nude photos of adults won&amp;#x27;t trigger it; only photos of already known CSAM content will trigger (and that too, Apple requires a specific threshold of matches before a report is triggered).&lt;p&gt;[1] &amp;quot;The threshold is selected to provide an extremely low (1 in 1 trillion) probability of incorrectly flagging a given account.&amp;quot; Page 4 of &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.apple.com&amp;#x2F;child-safety&amp;#x2F;pdf&amp;#x2F;CSAM_Detection_Technical_Summary.pdf&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.apple.com&amp;#x2F;child-safety&amp;#x2F;pdf&amp;#x2F;CSAM_Detection_Techni...&lt;/a&gt;</text></item><item><author>querez</author><text>I have a newborn at home, and like every other parent, we take thousands of pictures and videos of our newest family member. We took pictures of the very first baby-bath. So now I have pictures of a naked baby on my phone. Does that mean that pictures of my newborn baby will be uploaded to Apple for further analysis, potentially stored for indefinite time, shared with law enforcement?</text></item></parent_chain><comment><author>windexh8er</author><text>&amp;gt; The false positive rate for any given image is not 1 in a trillion. Perceptual hashing just does not work like that. It also suffers from the birthday paradox problem - as the database expands, and the total number of pictures expands, collisions become more likely.&lt;p&gt;There was a good article [0] that was on HN a couple days ago that touches on the flat out lie regarding &amp;quot;one in a trillion&amp;quot; and how PhotoDNA sounds poorly thought out.&lt;p&gt;[0] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.hackerfactor.com&amp;#x2F;blog&amp;#x2F;index.php?&amp;#x2F;archives&amp;#x2F;929-One-Bad-Apple.html&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.hackerfactor.com&amp;#x2F;blog&amp;#x2F;index.php?&amp;#x2F;archives&amp;#x2F;929-On...&lt;/a&gt;</text></comment>
<story><title>The deceptive PR behind Apple’s “expanded protections for children”</title><url>https://piotr.is/2021/08/12/apple-csam/</url></story><parent_chain><item><author>stickfigure</author><text>The false positive rate for any given image is not 1 in a trillion. Perceptual hashing just does not work like that. It also suffers from the birthday paradox problem - as the database expands, and the total number of pictures expands, collisions become more likely.&lt;p&gt;The parent poster does make the mistake of assuming that other pictures of kids will likely cause false positives. Anything could trigger a false positive - especially flesh tones. Like, say, the naughty pictures you&amp;#x27;ve been taking of your (consenting) adult partner. I&amp;#x27;m sure Apple&amp;#x27;s outsourced low-wage-country verification team will enjoy those.</text></item><item><author>fortenforge</author><text>Lots of people responding to this seem to not understand how perceptual hashing &amp;#x2F; PhotoDNA works. It&amp;#x27;s true that they&amp;#x27;re not cryptographic hashes, but the false positive rate is vanishingly small. Apple claims it&amp;#x27;s 1 in a trillion [1], but suppose that you don&amp;#x27;t believe them. Google and Facebook and Microsoft are all using PhotoDNA (or equivalent perceptual hashing schemes) right now. Have you heard of some massive issue with false positives?&lt;p&gt;The fact of the matter is that unless you possess a photo that exists in the NCMEC database, your photos simply will not be flagged to Apple. Photos of your own kids won&amp;#x27;t trigger it, nude photos of adults won&amp;#x27;t trigger it; only photos of already known CSAM content will trigger (and that too, Apple requires a specific threshold of matches before a report is triggered).&lt;p&gt;[1] &amp;quot;The threshold is selected to provide an extremely low (1 in 1 trillion) probability of incorrectly flagging a given account.&amp;quot; Page 4 of &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.apple.com&amp;#x2F;child-safety&amp;#x2F;pdf&amp;#x2F;CSAM_Detection_Technical_Summary.pdf&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.apple.com&amp;#x2F;child-safety&amp;#x2F;pdf&amp;#x2F;CSAM_Detection_Techni...&lt;/a&gt;</text></item><item><author>querez</author><text>I have a newborn at home, and like every other parent, we take thousands of pictures and videos of our newest family member. We took pictures of the very first baby-bath. So now I have pictures of a naked baby on my phone. Does that mean that pictures of my newborn baby will be uploaded to Apple for further analysis, potentially stored for indefinite time, shared with law enforcement?</text></item></parent_chain><comment><author>nonbirithm</author><text>Then where are the news reports or articles of these false positives that would have shown up within the past decade? That&amp;#x27;s how long these companies have been using PhotoDNA on the server side. And the version of PhotoDNA from ten years ago would probably have been inferior to the version in place now. Is there even a single verifiable report of such a false positive? I feel that with the amount of attention brought to this issue, if there was such a report then it probably would have been brought up by now.&lt;p&gt;Beyond that, assume that a false positive occurs and the innocent person is taken to court. Why would they have to fear being convicted if they don&amp;#x27;t actually hold any incriminating evidence? At most, that would become evidence &lt;i&gt;against&lt;/i&gt; using perceptual hashing in future court cases.&lt;p&gt;The issue in that case is the violation of the innocent person&amp;#x27;s privacy, not that they have a risk of being falsely convicted. The courts would still need admissible evidence, and I don&amp;#x27;t believe that only having a perceptual hash and a set of legally photographed images clears that bar.&lt;p&gt;However, it becomes a completely separate issue if the false positives are &amp;quot;coincidentally&amp;quot; used to persecute marginalized groups in other countries where the same set of laws don&amp;#x27;t apply. But Apple has stated that they have no intention of expanding the system&amp;#x27;s scope to follow those laws. There isn&amp;#x27;t any evidence yet that Apple will do such a thing, or that they&amp;#x27;ve already done it in the past. We are free to disbelieve them, but that&amp;#x27;s what they&amp;#x27;ve stated. We can only hope that they won&amp;#x27;t change their minds.</text></comment>