Turns out that Adobe is collecting all of its customers' pictures into a machine learning training set.

This is opt-out, not opt-in so if you use Lightroom, for example, it defaults to adding all of your photos to the set.

If these are unpublished pictures, work-in-progress, etc. they'll still be analysed as soon as they're synced.

I've been using Lightroom to sync photos from my Windows desktop to my iPad. Now I need to reconsider that.

This obviously only applies if the pictures touch Adobe's servers in some way, such as cloud syncing. That's basically every picture ever uploaded into Lightroom.
@baldur I’m assuming this means those of us on Lightroom Classic are exuded the invasion. Fml.
@jonpainterphoto @baldur Yes, unless you sync a LR Classic catalog or collection up to the Adobe Cloud service for use with Lightroom mobile, which I'm sure some folks have done for convenience. The fact that you have to opt out in the website instead of inside any of the applications is pretty problematic.

@paulrcoen @baldur Huh. If you're on a large account - say you receive CC as a student at a college - you may not have access to opt out.

Presumably the institution has decided one way or the other, and users have no choice.