I don't understand the claim that this system improves their ability to detect anything. If it's really true that the system only works on data uploaded to icloud then apple could have easily just done all the scanning in the cloud, because icloud is not end-to-end encrypted. In that case, all this feature does is move the computational cost of scanning from Apple's datacenters to Apple's users, saving Apple money and costing users battery life. It doesn't change anything about how effective the scanning can be. Unless I misunderstand how it works.