This article explains how to hide photos on iPhone.

The Photos app that comes preinstalled on every iPhone has built-in tools that let you hide photos on your iPhone (or iPod touch, or iPad). There are two ways to hide photos, depending on which version of iOS you're running.

Once you’ve selected a photo, you can hide it with two taps. Here’s what you need to do:

Select a photo using the built-in iOS Photos app.