you’re free to use any image you have in Photos.
Some people like to find a set of pictures they like and customize their phone around those pictures.
On newer versions of the iPhone, this app is probably already installed.

On older iPhones, you may need to download it from the Apple App Store.
hit the+(plus) icon in the upper right corner of the Shortcuts app.
On theNew Shortcutpage that appears, tapAdd Action.
From theActionssection of the search results, tapOpen App.
Then in theScriptingsection of theNew ShortcuttapChoose.
Scroll through the list of available apps and choose the one you want to create a customized shortcut for.
You return to theNew Shortcutpage, and the name of the app now appears in theScriptingsection.
Tap the three-dot menu near the top right corner.
TapAdd to Home Screen.
The tap the icon for the shortcut.
You could also tapTake Photohere and take a photo to use as the image for the app icon.
Navigate to and snag the image you want to use as your app icon.
When you’re done, tapChoose.
Repeat this process for each of the apps you want to change on your home screen.