Flock has knowledge/use of the data. Their system processes can relate the photos “owned” by two different entities. They’re interacting with it and selling their access to it as a feature. That’s obviously distinct from S3.
But you knew that.
But you knew that.
They're contractually forbidden from "selling their access to it" to arbitrary parties; they can share data only with the consent of their customers, almost all of whom actively want that data shared --- this is a very rare case of a data collection product where that's actually the case.
This is the same situation as a web hosting provider: if it is communicated to them that one of their customers uses their service to host illegal content, then it becomes the web hosting provider's responsibility to remove that content.
Reasonable technical feasibility for the service provider is key here, but it can be argued since the data can apparently be shared in ways that identify OP.
Probably not how the law currently works (don't know, not a lawyer), but I guess it should, as otherwise it allows creating a platform that shares abusively retained data without any reasonable recourse for the subjects of this data to remove the data from the platform.
If I as a photographer take a photograph of someone, the photo does not belong to that person—the photographer retains the IP and ownership rights.
You have rights too, such as privacy/likeness rights, which allow you to restrict what the IP owner is allowed to do with the image that they own, but you do not own the data, and your rights give you a claim against the data owner.
Flock probably have legal obligations or contractual commitments not to delete or destroy their customers' data, and changing that is not necessarily a good thing.
As such, even if they can contract it such that they are not legally responsible for such use, they are very much knowingly facilitating it. If this was physical goods, rather than data, they would probably been as responsible as their customers.
Flock knowingly collects PII of people they have no direct relationship with, and transfers it to third parties. If that transfer, which Flock seem to gain from, is legally a sale is something to be argued at a great expense in front of the court.
But regardless of that definition, I so think that any reasonable person (= not a corporate lawyer) would consider there is a sale of data here.