Live Photos is a feature on recent iPhones that adds a small video clip before the still image and also a small video clip after the still image when taking a picture with the camera app.
Live Photos can be a great feature, especially when editing (enabling the still image to be changed e.g. if the subject’s eyes are closed, to open in another frame) however, some people either do not like Live Photos or cannot afford the extra memory they consume. In iOS 11 turning off Live Photos in the camera app only lasts for the current session of camera use and automatically turns back on the next time the camera app is activated.
There is a setting that can prevent this and permanently disable Live Photos.
Select the settings app on your iOS device (img.1).
Once the setting screen is displayed scroll down until the camera settings option is visible then tap this (img.2).
In the camera settings select the Preserve Settings option (img.3).
Now turn on Live Photo, this sounds counterintuitive but this setting tells the iPhone to remember the state you have chosen for Live Photos (img.4).
Leave the settings app and enter the camera app, make sure the photo mode is showing then tap the Live Photo icon so it appears white with a strike through (img.5).
Live Photos is now disabled for every future use of the app.