Privacy

It's already happened where identity providers had a data leak, and it has been exposed the extensive surveillance they participate in. You can't trust these companies with your data.

Age verification vendor Persona left frontend exposed

researchers found details about the extensive surveillance Persona software can perform. Beyond checking their age, the software can perform 269 distinct verification checks, run facial recognition against watchlists and politically exposed persons, screen “adverse media” across 14 categories (including terrorism and espionage), and assign risk and similarity scores.

Persona collects—and can retain for up to three years—IP addresses, browser and device fingerprints, government ID numbers, phone numbers, names, faces, plus a battery of “selfie” analytics like suspicious-entity detection, pose repeat detection, and age inconsistency checks.

Never upload your government ID and selfie; it's an extreme risk to your online privacy. In recent years, and depending where you live, it could be a risk to your physical safety as well. First thing that came to my mind is detecting whether the user "looks [gender] enough" to detect transitions.