Controlling the Screenshot in the iOS Multitasking Switcher

In the App Programming Guide for iOS (opens new window):

Remove sensitive information from views before moving to the background.

When an app transitions to the background, the system takes a snapshot of the app’s main window, which it then presents briefly when transitioning your app back to the foreground.

Show an Image for Snapshot

public override void DidEnterBackground(UIApplication application)
 {
    //to add the background image in place of 'active' image
    var backgroundImage = new UIImageView();
    backgroundImage.Tag = 1234;
    backgroundImage.Image = UIImage.FromBundle("Background");
    backgroundImage.Frame = this.window.Frame;
    this.window.AddSubview(backgroundImage);
    this.window.BringSubviewToFront(backgroundImage);
}

public override void WillEnterForeground(UIApplication application)
{
    //remove 'background' image
    var backgroundView = this.window.ViewWithTag(1234);
    if(null != backgroundView)
        backgroundView.RemoveFromSuperview();
}

Remarks

Adapted from actual StackOverflow Question Controlling the Screenshot in the iOS7 Multitasking Switcher (opens new window) and answer Obj-c Answer (opens new window)