Vector Images Tutorial for Xcode 9: https://github.com/jgonfer/vector-images-tutorial-xcode

AccessibilityViewController.swift

override func viewDidLoad() {
    super.viewDidLoad()
        
    if #available(iOS 11.0, *) {
        pumpkinPngImageView.adjustsImageSizeForAccessibilityContentSizeCategory = true
        pumpkinPdfImageView.adjustsImageSizeForAccessibilityContentSizeCategory = true
    } else {
        // Fallback on earlier versions
    }
}

ImagesViewController.swift

override func viewDidLoad() {
    super.viewDidLoad()
        
    if #available(iOS 11.0, *) {
        let image = UIImage(named: "first_large")
        imagesBarItem.largeContentSizeImage = image
    } else {
        // Fallback on earlier versions
    }
}