Storing an image from the web for one session (in Swift)

I am following a tutorial about getting images from the web and storing them on the phone in Swift. For my purpose, I would like to know how I could only store them for one 'session', which means until the user stops using the app. The reason is that I want to change the image of the url every day. Anyone any idea?

  @IBOutlet var overLay: UIImageView!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.



    let url = NSURL(string: "http://test.com")

    // Update - changed url to url!

    let urlRequest = NSURLRequest(URL: url!)

    NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue(), completionHandler: {
        response, data, error in

        if error != nil {

            println("There was an error")

        } else {

            let image = UIImage(data: data)

            // self.overLay.image = image

            var documentsDirectory:String?

            var paths:[AnyObject] = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.UserDomainMask, true)

            if paths.count > 0 {

                documentsDirectory = paths[0] as? String

                var savePath = documentsDirectory! + "/overLay.jpg"

                NSFileManager.defaultManager().createFileAtPath(savePath, contents: data, attributes: nil)

                self.overLay.image = UIImage(named: savePath)

            }

        }


    })

}

thank you so much!