Set all back buttons like leftBarButtonItem with custom image

Question

How do I set a custom image to all back buttons of view controllers pushed in a UINavigationController?

My issues are:

• must look like leftBarButtonItem, position-wise (because the backBarButtonItem itself is too glued to the left and I can't seem to change it's horizontal alignment).
• has to be on all back actions (instead of manually setting on each view controller).
• having a method setCustomBackButton and calling it on each view controller is also not an option, I'm looking for something like UINavigationBar.appearance(), i.e., throughout the app.

Something like this: But with the back action working without me manually setting the selector on each view controller.

UPDATE: In response to Joe's solution, I'm getting that error:

Answer 1

UINavigationBar.appearance().backIndicatorImage = UIImage(named: "backArrow")

See Here: https://www.raywenderlich.com/108766/uiappearance-tutorial