Swipe your camera roll clean.
Yes. Culla never permanently erases anything. Photos you confirm go to Recently Deleted in the Photos app, where they stay recoverable for 30 days. Open Photos → Collections → Utilities → Recently Deleted, select the photo, and tap Recover.
Culla analyses your library on-device the first time you open it, and grouping only appears once that finishes. On a large library this takes a little while — the Home screen shows a progress indicator while it runs. Groups also need genuinely similar photos: if your library has no near-duplicates, everything correctly shows as a solo shot.
That's deliberate. Culla gives you five minutes of cleaning a day, because clearing a camera roll works better as a small daily habit than as a marathon you abandon halfway. You can choose a shorter session length in Settings.
Culla can only see the photos you selected, so grouping has much less to work with. To change it: Settings → Apps → Culla → Photos → Full Access.
No. All analysis runs on your iPhone, there is no account, and the app makes no network requests at all. See the privacy policy.
During a session, tap the undo arrow between the two buttons. After a session, every marked photo appears on the review screen — tap any one to keep it instead. Nothing is deleted until you tap the confirm button and approve the iOS dialog that follows.