How to put an image as the navigation bar title

Set the navigationItem's titleView

UIImage *image = [UIImage imageNamed:@"image.png"];
self.navigationItem.titleView = [[UIImageView alloc] initWithImage:image];

Swift 4.2
Includes suggested framing/scaling

let image: UIImage = UIImage(named: "image.png")!
let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 40, height: 40))
imageView.contentMode = .scaleAspectFit
imageView.image = image
self.navigationItem.titleView = imageView

You can change all the views in a UINavigationBar. If you are trying to alter the navigationBar in a navigation controller do:

self.navigationItem.titleView = [[[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image.png"] autorelease];

If you are creating the navigationBar yourself do the same, but in stead of calling self.navigationItem call: navigationBar.topItem

In case if someone needs both image and text inside the Navigation bar title view in Swift 4.2, please try this function:-

override func viewDidLoad() {

    super.viewDidLoad()

    //Sets the navigation title with text and image
    self.navigationItem.titleView = navTitleWithImageAndText(titleText: "Dean Stanley", imageName: "online")
}

func navTitleWithImageAndText(titleText: String, imageName: String) -> UIView {

    // Creates a new UIView
    let titleView = UIView()

    // Creates a new text label
    let label = UILabel()
    label.text = titleText
    label.sizeToFit()
    label.center = titleView.center
    label.textAlignment = NSTextAlignment.center

    // Creates the image view
    let image = UIImageView()
    image.image = UIImage(named: imageName)

    // Maintains the image's aspect ratio:
    let imageAspect = image.image!.size.width / image.image!.size.height

    // Sets the image frame so that it's immediately before the text:
    let imageX = label.frame.origin.x - label.frame.size.height * imageAspect
    let imageY = label.frame.origin.y

    let imageWidth = label.frame.size.height * imageAspect
    let imageHeight = label.frame.size.height

    image.frame = CGRect(x: imageX, y: imageY, width: imageWidth, height: imageHeight)

    image.contentMode = UIView.ContentMode.scaleAspectFit

    // Adds both the label and image view to the titleView
    titleView.addSubview(label)
    titleView.addSubview(image)

    // Sets the titleView frame to fit within the UINavigation Title
    titleView.sizeToFit()

    return titleView

}

Updated with Swift 2.x

navigationItem.titleView = UIImageView.init(image: UIImage(named:"yourImageName"))