Set image as background

ViewController.swift

import UIKit

class ViewController: UIViewController {
    
    var imageView: UIImageView?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let screenSize: CGRect = UIScreen.mainScreen().bounds
        
        if let image = UIImage(named: "autumn.jpg") {
            imageView = UIImageView(image: image)
            imageView!.frame = screenSize
            view.addSubview(imageView!)
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

}