Yep, Apple currently only scans iCloud Mail attachements (I believe they confirmed this, don't have the source at hand though), which explains the discrepancy.

Yep, Apple currently only scans iCloud Mail attachements (I believe they confirmed this, don't have the source at hand though), which explains the discrepancy. There's a big difference though between scanning a library (which is closer to what DropBox/OneDrive are doing) and when it's messaging platform whose ultimate goal is communication between people. It does make sense that those catch way more. If Apple had roll those scans on iMessage attachements (which they didn't planned to, though the feature looked to be designed for it way more than it was for a library scan), you would probably see comparable numbers (modulo those platforms relative marketshares). One big problem though is are those large numbers actually actionable ? I think I remember seeing a quote from Swiss (?) law enforcement that complained that the reports they got from NCMEC were nearly all of the time unactionable. There are possibly many reasons from this, it could be differences in local laws, algorithms that wrongly report things, or other factors (maybe not enough to identify the user of the acount, etc). This is where one feature of Apple's design was a bit better: they didn't plan to report every single occurence, but would only if 30 such images were detected. Part of the reason they did was because of the imperfections of the NeuralHash mechanism, sure, but in the end it doesn't matter. One can argue doing this would at least generate more actionnable reports. It shouldn't be a numbers game.