> Thorn, the non-profit behind Safer, says it spots the content with greater than 99% precision.

Sounds like it's claiming 99% precision, so 99% of positives are true positives.

Recall probably isn't great, because (a) if it were great they'd brag about it and (b) you don't get to 99% precision without sacrificing some recall.

Seems reasonable to aim high on precision, though, to avoid burying NCMEC in mis-classified data and also to avoid wrongly banning users' content.

https://sg.news.yahoo.com/2019-05-31-sex-lies-and-surveillan... I don't trust Thorn.

What in that article specifically makes you not trust Thorn? They seem to me like they're trying to do good work -- preventing child exploitation -- that necessarily involves partnering with organizations whose values won't always exactly line up with theirs.