This still relies upon some degree of compliance by Apple in order to acquire the stream of vouchers. Or alternatively a working security breach of Apple's syst

This still relies upon some degree of compliance by Apple in order to acquire the stream of vouchers. Or alternatively a working security breach of Apple's systems. Either way this represents an additional, non-trivial barrier to overcome. It would be interesting to know what the "chaff" rate is and whether any intelligence agency could stomach that amount of surveillance, particularly since it's by no means certain that any of them are real. In fact it seems to me that it's very unlikely indeed, especially if the material is in any way radioactive. After all, finding a match this way requires quite a few assumptions: 1. The target owns an iPhone; 2. The target has enabled iCloud Photo Library; 3. The target has a photo library small enough, or is paying for sufficient iCloud storage space, that the flagged images are included in the (sub)set stored in the cloud; 4. The target has imported the flagged images into their photo library rather than to iCloud Drive or any third party app like SpiderOak, Mega or Tresorit.