Help with existing app with many users, i want to add photo

Took me awhile to realize you were taking about 'U’nique 'I’D instead of 'U’ser 'I’nterface. Anyway, not quite following what you want, but it might help if you give us a better idea of how you data is laid out and how you want to link a profile to a photo using UUID. I feel Unique ID (UUID) should only be created when adding a record. If you have existing records, then I recommend finding a UUID generator online to fill the existing records.