But that's the rub. The system doesn't identify the photo, the user does. Imagine a photo service with Gmail-like filters, and I create a filter which says "If Photo Longitude/Latitude within this bounds, then photo is #GrangarsHouse". I've now turned a system with a general purpose EXIF metadata filter function into a system which can categorize locations that identify people's dwellings with high probability.

"Identifying" a purpose could range from simply clustering visually similar photos using any number of non-machine-learning, non-biometrically-aware image processing algorithms, to using DNNs like FaceNet, or using the old eigenvector facial recognition algorithms of the 90s.

As soon as I upload a photo I took of you to a photo hosting system that has any kind of search functionality at all, the risk is raised that you can be categorized and identified somehow. Really, "consent" was broken not by the company, but by the uploader.

I really think the genie's out of the bottle on photos now. So many people are constantly photographing on their phones, and so many are uploading them to publicly accessible feeds all over the internet, that a federated crawler could already be built to track you, in fact, I think there's already some social media monitoring services that offer this.

If you're out in public, you should pretty much assume you have no privacy with regards to your imagery, GDPR isn't gonna save you. You can control your own photos, but you can't control what other people do of photos taken of you.