Does hiding a photo remove it from iCloud?

No. The Photos Hidden album syncs like any other album. Only moving the photo into a vault app and deleting the original removes it from iCloud Photos.

What happens if I forget the vault passcode?

The vault is encrypted with it, so neither we nor Apple can open it. Write the passcode down when you set it, and use the app’s export to keep a backup.

Can a vault app see my photos?

Our vaults keep everything on the device. Nothing is uploaded unless you use an export or cloud option yourself.

How to hide photos on iPhone, properly

What the built-in Hidden album does

Select a photo, tap the share button, choose Hide. The photo moves to the Hidden album under Utilities in the Albums tab. On iOS 16 and later you can require Face ID to open that album: go to Settings → Apps → Photos and turn on Use Face ID. You can also hide the album itself from the Albums list with the Show Hidden Album switch.

For most people that is enough to keep a photo out of casual view. It is not enough if the phone is unlocked and someone is scrolling, or if the photo must stay out of iCloud Photos and shared devices.

Where it falls short

Hidden photos still sync to every device signed in to your iCloud Photos, including a family iPad.
They still appear in some photo pickers, Memories and search results.
A hidden photo is one tap from visible again. There is no separate passcode, no decoy, no record of attempts.
Videos and documents you did not take with the camera (screenshots, downloads, PDFs) are mixed into the same library.

Locking photos with a vault app

A vault app keeps its own encrypted store inside the app's sandbox. Photos you import into it are not part of the Photos library at all, so they do not sync, do not show in pickers, and open only with the vault's passcode or Face ID. The steps are the same in any of ours:

Install the vault and set a passcode. Turn on Face ID if you want it, but keep the passcode written somewhere safe; it is the only way back in.
Import from Photos. The vault copies the items into its store.
Delete the originals from Photos when the app asks, then empty Recently Deleted (Albums → Utilities → Recently Deleted → Select → Delete All). Until you do, the originals are still on the phone for 30 days.
Check iCloud Photos on another device a few minutes later to confirm the items are gone there too.

Settings worth turning on

Decoy password (Locksy): a second passcode that opens an innocent, empty vault.
Break-in alerts: the vault takes a photo with the front camera when a wrong passcode is entered and logs the time.
Hide from the app switcher: the vault blanks its preview when you swipe between apps.
Backup: vault content is not in iCloud Photos, so it is not in your photo backup either. Use the app's own export to keep a copy somewhere you control.

Which of our apps to use

All three do the core job. Locksy has the decoy password and per-album passcodes. iVault also takes files, documents and contacts. Hide Photos & Videos is the simplest of the three. Each is free to download with optional in-app purchases.