UIButton with an image. Scale: aspect fit.

Updated with Xcode 8.0/Swift 3 (September 19, 2016): 

override func viewDidLoad() {

    super.viewDidLoad()

        

    let image = UIImage(named: "image.png")

    let button = UIButton(frame: CGRect(x: 100, y: 100, width: 200, height: 200))

    button.imageView?.contentMode = UIViewContentMode.scaleAspectFit

    button.setImage(image, for: UIControlState.normal)

    button.addTarget(self, action: #selector(buttonPressed), for: UIControlEvents.touchUpInside)

    view.addSubview(button)

}

    

func buttonPressed() {

    print("button pressed!!")

}

Updated with Xcode 7.1.1/Swift 2.1 (November 12, 2015): 

    override func viewDidLoad() {

        super.viewDidLoad()

        

        let image = UIImage(named: "image.png")

        let button = UIButton(frame: CGRectMake(100, 100, 200, 200))

        button.imageView?.contentMode = UIViewContentMode.ScaleAspectFit

        button.setImage(image, forState: UIControlState.Normal)

        button.addTarget(self, action: "buttonPressed:", forControlEvents: UIControlEvents.TouchUpInside)

        self.view.addSubview(button)

    }

    

    func buttonPressed(sender: UIButton) {

        print("button pressed!!")

    }

Original post (December 17, 2014): 

   override func viewDidLoad() {

        super.viewDidLoad()

        

        let image = UIImage(named: "image.png") as UIImage!

        let button = UIButton.buttonWithType(UIButtonType.System) as UIButton

        button.frame = CGRectMake(100, 100, 200, 200)

        button.imageView?.contentMode = UIViewContentMode.ScaleAspectFit

        button.setImage(image, forState: .Normal)

        button.addTarget(self, action: "buttonPressed:", forControlEvents: UIControlEvents.TouchUpInside)

        self.view.addSubview(button)

    }

    func buttonPressed(sender: UIButton) {

        println("button pressed!!")

}