How to lock your photo gallery on Android
The problem is almost always the same: the phone is unlocked and in someone else's hands. Android has two different answers to that, they protect different things, and picking the wrong one leaves the photos you meant to hide sitting in the grid.
Decide which problem you have
Two situations get called the same thing, and they need opposite solutions.
- A few photos nobody should see. You want those specific pictures out of the grid, out of search, and out of anything that syncs. The rest of the gallery can stay open.
- The gallery itself should not open. You hand your unlocked phone to someone to show them one thing, and you do not want a stray tap landing in your photos at all.
The first wants a locked folder. The second wants an app lock. Neither one does the other's job, and that is the mistake worth avoiding.
Option 1: Locked Folder, for particular photos
Google Photos has a Locked Folder, and on Pixel phones the camera can send a shot straight into it. Anything inside is kept out of the main grid, out of search, out of memories, and out of other apps that ask for your photos.
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In Google Photos, open Collections, then Locked Folder.
Set it up the first time with your screen lock or fingerprint.
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Move photos in.
Select them in the grid, then choose Move to Locked Folder from the menu.
Read this part before you move anything. On older versions the Locked Folder was local to the phone and its contents were not backed up, so a lost phone meant lost photos, and moving something in could remove the backed up copy. Google has since added backup for it, but whether it applies to you depends on your app version and your account. Check what your own phone says on the Locked Folder setup screen before you move the only copy of anything into it.
Option 2: an app lock, for the whole gallery
An app lock puts the fingerprint prompt in front of the app itself. It does not hide any individual photo, and it is not trying to: it stops the app opening at all on a phone that is already unlocked.
Samsung phones have this built in through Secure Folder, which is a genuinely separate encrypted space with its own copy of the gallery. It is thorough, and the cost of that thoroughness is that the contents live in a parallel world: the photos are not in your normal gallery, and getting them in and out is a deliberate move each time.
On phones without it, the lock has to come from the gallery app you use. A gallery that asks for the fingerprint before it opens covers the everyday case, which is the phone being handed over unlocked.
The part people forget: the recent apps preview
A lock on the app is worth very little if the last thing you were looking at is sitting in the app switcher as a thumbnail. Swiping up shows a preview of every recent app, and by default a gallery's preview is a photo.
Android has a flag for this, FLAG_SECURE, which tells the system a screen must not
be captured. When an app sets it, the recent apps preview goes blank and screenshots of that
screen are refused. It is worth checking that whatever you are relying on actually sets it,
because a lock without it leaks the thing it was locking.
What none of this protects against
All of the above assumes somebody holding your unlocked phone and poking at it. It is the right threat to plan for, because it is the one that actually happens.
It is not protection against someone with your screen lock code, and on most phones the app lock and the phone lock are the same fingerprint. It is also not encryption of the file: a photo behind an app lock is still an ordinary file on the storage, and something with real access to the device can read it. Samsung's Secure Folder is the exception, because it is a separate encrypted profile rather than a prompt in front of an app.