Ideally all of it, but album is the primary case. Sidecar files would be fine, or an sqlite3 schema, or even a CSV if it meant scripting recreation of e.g. a li

Ideally all of it, but album is the primary case. Sidecar files would be fine, or an sqlite3 schema, or even a CSV if it meant scripting recreation of e.g. a link farm from photos as sharded images to directories of albums. Tags, that's just icing on the cake for me. That said, exif compatible metadata for date helps a LOT.