[sneak]

It also allows them to track the contact/social graph of all users based on clusters of who has the same unique file hashes.

Then again, they already have everyone's address books and iMessage traffic, so I guess they already have that data for most of the industrialized world. I wonder who else will preserve copies?

[smoldesu]

100% - this was my largest concern when they announced perceptual hashing, and it seems to be the big takeaway here. Of course, this is a concern with most online hosting services, but at Apple's scale it's pretty scary to consider the possibilities.