If a friend clicks a photo of me and uploads it to Google Photos, IMO, it's not okay for Google to use my face to train models without explicit permission from me. Unfortunately, as is often the case with technology, laws have not kept up with the lastest developments, and likely will not in my country for several more decades. Welp.
Just to be pedantic in the spirit of HN. Google isn't training models w/your face from your photo library. The way face recognition works is that Google would collect a dataset somehow and label that for the various feature and train a model for face recognition. Usually this is done with a carefully curated dataset that would be sure to include various ages, genders, ethnicities, lighting conditions, angles, and cam…
You can't do "celebrity" recognition from a generalized data set.