NSUserDefaultsにUIImageの配列を保存できません

SecondViewControllerで配列にUIImageを保存したいです。
まず、SecondViewControllerで写真を配列[imageFile]に保存します。

import UIKit
    var imageFile = [UIImage]()
    class SecondViewController: UIViewController,UINavigationControllerDelegate,UIImagePickerControllerDelegate {

        override func viewDidLoad() {
            super.viewDidLoad()

            if UIImagePickerController.isSourceTypeAvailable(UIImagePickerControllerSourceType.PhotoLibrary){
                let pho = UIImagePickerController()
                pho.delegate = self
                pho.sourceType = UIImagePickerControllerSourceType.PhotoLibrary
                self.presentViewController(pho, animated: true, completion: nil)
            }
        }
        var original:UIImage!

        @IBOutlet weak var imageView: UIImageView!

    func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {
            if info[UIImagePickerControllerOriginalImage] != nil{
                original = info[UIImagePickerControllerOriginalImage] as? UIImage
                imageView.image = info[UIImagePickerControllerOriginalImage] as? UIImage
            }
            picker.dismissViewControllerAnimated(true, completion: nil)
        }
        override func didReceiveMemoryWarning() {
            super.didReceiveMemoryWarning()
            // Dispose of any resources that can be recreated.
        }


        @IBAction func save(sender: UIButton) {
            imageFile.append(original)

            NSUserDefaults.standardUserDefaults().setObject(imageFile, forKey: "Key")
        }

    }

次にFirstViewControllerで保存したものを受け取りたいのですが
SecondViewControllerのsaveボタンを押したらエラーが出ます。
他のプログラムでも同じことをしましたができませんでした。
文字の配列では、できました。
NSUserDefaultsではUIImageの配列は扱えないのでしょうか？

import UIKit

        class FirstViewController: UIViewController {

            override func viewDidLoad() {
                super.viewDidLoad()
                // Do any additional setup after loading the view, typically from a nib.
                if NSUserDefaults.standardUserDefaults().arrayForKey("Key") != nil{

                    imageFile = NSUserDefaults.standardUserDefaults().arrayForKey("Key") as! [UIImage]

                }

            }

            override func didReceiveMemoryWarning() {
                super.didReceiveMemoryWarning()
                // Dispose of any resources that can be recreated.
            }
            @IBOutlet weak var label: UILabel!
            @IBAction func load(sender: UIButton) {
            label.text! = String(imageFile.count)
            }

        }