UIImageView with Aspect Fit and Alignment To Top. thanks to (http://stackoverflow.com/a/27569222/1267174)

UIImageView+topAlignmentAndAspectFit

extension UIImageView {
    func topAlignmentAndAspectFit(to view: UIView) {
        self.contentMode = .scaleAspectFill
        self.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(self)
        
        self.addConstraints(
            [NSLayoutConstraint(item: self,
                                attribute: .height,
                                relatedBy: .equal,
                                toItem: self,
                                attribute: .width,
                                multiplier: self.frame.size.height / self.frame.size.width,
                                constant: 0.0)])
        view.addConstraints(
            [NSLayoutConstraint(item: self,
                                attribute: .centerX,
                                relatedBy: .equal,
                                toItem: view,
                                attribute: .centerX,
                                multiplier: 1.0,
                                constant: 0.0)])
        view.addConstraints(
            [NSLayoutConstraint(item: self,
                                attribute: .width,
                                relatedBy: .equal,
                                toItem: view,
                                attribute: .width,
                                multiplier: 1.0,
                                constant: 0.0)])
        view.addConstraints(
            NSLayoutConstraint.constraints(withVisualFormat: "V:|[imageView]",
                                           options: .alignAllTop,
                                           metrics: nil,
                                           views: ["imageView": self]))
    }
}