Back Button Image - what is it called in Swift?

Try to add custom view as back button like as

var backButton = UIButton(frame: CGRectMake(0, 0, 70.0, 70.0))
var backImage = UIImage(named: "backBtn")
backButton.setImage(backImage, forState: UIControlState.Normal)
backButton.titleEdgeInsets = UIEdgeInsetsMake(10.0, 10.0, 10.0, 0.0)
backButton.setTitle("Back", forState: UIControlState.Normal)
backButton.addTarget(self, action: "buttonPressed", forControlEvents: UIControlEvents.TouchUpInside)
var backBarButton = UIBarButtonItem(customView: backButton)

var spacer = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.FixedSpace, target: nil, action: nil)
spacer.width = -15

self.navigationItem.leftBarButtonItems = [spacer,backBarButton]

It will look same as iOS back button

I struggled with this question for a while. Finally I got the back image with the following code:

let backImage = navigationController?.navigationBar.subviews[2].subviews[0].subviews[0].subviews[0] as! UIImageView).image

Before run the code above, make sure the back button is showing. Then you can save backImage to anywhere you want.

Here is the backImage I got.