http://swonderstzr43aczpcwdoyc25vwxngyromja7pyb5sf26ap3v535sxqd.onion/resources/facebook-adding-metadata-hiding-special-instructions-in-photos
The ability to assign unique references attached to content and associate this with a “person” via an account (or a device) provides mechanisms to track and gather information in a way that can learn patterns, infer relationships, behavioural analysis and for forensic purposes.