If you scan 1,000,000 pictures (with let's say 10 CSAM), you'll have 100 false positives and 10 true positives, giving you like only 10% correct results
replyAh, sorry, I misread what the OP meant by "matches" - thought they were referring to all classifier outputs, while they specifically meant the positives. I changed my original comment to better reflect what I meant, even though that makes it a bit of a non-sequitur now.
replyHow many child abusers do you think there are out there?
replyEven if 10% of population were actively criminal pedos (which is waaaay too high), its pretty safe to assume that the majority of even their online footprint would be ordinary images/messages.
replySo a quota of 0.1% or even less material being detectably criminal sounds realistic (probably not much less, though).