Summary: We don’t currently have a facility to alert you if you have or have not uploaded a photo before. It’s not a common use case, and it doesn’t break anything in the database or overwrite a previous Encounter photo (even by the same name) in the database. You can absolutely upload a previous photo again as a new Encounter and even match it against itself without losing previous data.
Database context (photos already assigned to Encounters): when an Encounter is created, photos get UUIDs and are stored uniquely in folders under those UUIDs. We don’t check whether we have seen the photo before, but we also don’t overwrite any other photo whether it has the same content and/or the same name.
Bulk upload context: after login, when you upload photos for any particular spreadsheet, we store these new photos and any photos you have uploaded before in a giant bucket under your username. In this context a new photo by the same name should overwrite the old photo before the new upload begins. Once the upload begins, the photo is assigned a UUID and copied into a separate folder for long-term storage with the Encounter.
There’s even more nuance to it than the above in terms of how we address photos in the computer vision context, but generally duplication of a photo is uncommon across Wildbooks, and where encountered, it does not break anything. We leave it up to users to track what offline data has been uploaded to Wildbook.