This category "UIViewController+NavigationBar" is a helper to

1. Set the title of back button in navigation bar
2. Set image as the title view in navigation bar

1. Copy the UIViewController+NavigationBar.h/.m to your project.
2. Import the "UIViewController+NavigationBar.h" in your UIViewController.
3. The category methods are ready to use NOW.

Create a backBarButtonItem for the previous ViewController.

Check this post iOS Set Navigation Bar Back Button Title for more insight into setting the back button title,

Set Image as the NavigationItem titleView; if image height > 44, resize it.

https://developer.apple.com/library/ios/documentation/uikit/reference/UINavigationController_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40006934-CH3-SW25