Override back button without bullet frame

gistfile1.txt

UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithTitle: @" " style:UIBarButtonItemStylePlain target:nil action:nil];
self.navigationItem.backBarButtonItem = backButton;
UIImage *backButtonImage = [[UIImage imageNamed: @"img-arrow-left"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 4, 0, 36)];
[[UIBarButtonItem appearance] setBackButtonBackgroundImage:backButtonImage forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];