func animate(_ image: UIImageView) {
UIView.animate(withDuration: 1.0, delay: 0.0, options: [.curveLinear],
animations: {image.center.x -= 10},
completion: {_ in self.animate(image)})}

func animate(_ image: UIImageView) {
    UIView.animate(withDuration: 5, delay: 0, options: .curveLinear, animations: {
        image.transform = CGAffineTransform(translationX: -100, y: 0)
    }) { (success: Bool) in
        image.transform = CGAffineTransform.identity
        animate(image)
    }
}

func animateBackground() {

    // Animate background
    // cityImage is the visible image
    // cityImage2 is the hidden image

    UIView.animate(withDuration: 12.0, delay: 0.0, options: [.repeat, .curveLinear], animations: {
        self.cityImage.frame = self.cityImage.frame.offsetBy(dx: -1 * self.cityImage.frame.size.width, dy: 0.0)
        self.cityImage2.frame = self.cityImage2.frame.offsetBy(dx: -1 * self.cityImage2.frame.size.width, dy: 0.0)
    }, completion: nil)

}