NSImageView with rounded corners

roundedCorners.swift

// XCode 8.3
// Swift 3.1

import Cocoa

class SomeViewController: NSViewController {
  @IBOutlet weak var artwork: NSImageView!
  
  override func viewDidLoad() {
    super.viewDidLoad()
    artwork.wantsLayer = true // Use a layer as backing store for this view
    artwork.canDrawSubviewsIntoLayer = true // Important, flatten all subviews into layer
    artwork.layer?.cornerRadius = 4.0
    artwork.layer?.masksToBounds = true // Mask layer
  }
}