Customize Back Button of Navigation Controller

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
[button setImage:[UIImage imageNamed:@"back.png"] forState:UIControlStateNormal];
[button addTarget:self action:@selector(btnSearchBackAction:) forControlEvents:UIControlEventTouchUpInside];
[button setFrame:CGRectMake(0, 0, 32, 32)];