You have a few photos that shouldn’t be visible in the normal photo overview on the iPhone or iPad? With iOS 12 you have the possibility to hide photos easily.
First of all: they are actually only hidden, i.e. taken out of the photo media library. They can still be found in an extra folder, are accessible when the iPhone is unlocked and are also synchronized via the photo stream. So rather something to create more privacy, if you are connected to an Apple TV via AirPlay and some photos shouldn’t appear instead of a super secure storage for secret documents.
Hiding photos is quite simple: select a photo and then tap the share icon in the lower left corner. Now search in the bottom row for the option Hide. Confirm this again and the photo is gone from the normal photo overview.
But as I said you can still find the pictures in the “Hidden” folder. This can be undone in the same way, only then with the option Unhide. So have fun now with withholding some of your more interesting photos from the public. 😉