What we think might be easy and intuitive others users are sometimes impressed so ...
How to Set Any Picture as Background Wallpaper on iPhone & iPad:
1 Open the “Photos” app and browse to the picture you want to set as the background wallpaper image
2 Tap on the sharing button, it looks like a box with an arrow flying out of it
3 Tap on the “Use as Wallpaper” button option
4 Arrange the picture as desired, then click on “Set”
5 Choose “Set Home Screen” to set the picture as the background image of the device (or choose ‘Set Lock Screen’ set it as the picture on the locked device where the clock shows)
6 Exit out of Photos app and return to the Home Screen by pressing the Home button, you’ll see the background of the iOS device has been set as the picture you chose