How do capture screenshot or create bitmap of non active window in C# winforms

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C#6.0

I have create bitmap of winform window by using TakeSnapshot(Control ctl) and BitmapToImageSource(Bitmap bitmap)method.
This code is work for Active window but not work for non active window.
Non active window bitmap is with active window portion which spread on it.
How to create bitmap of Non active window?

What I have tried:

public void CreateImagesOfCurrentOpenWindows()
{
  foreach (Form frm in Application.OpenForms)
  {
    var bitmap1 = TakeSnapshot(frm);
    //var bitmapImage = BitmapToImageSource(bitmap1);

    bitmap1.Save("" + frm.Name + "", System.Drawing.Imaging.ImageFormat.Jpeg);
  }
}

public static Bitmap TakeSnapshot(Control ctl)
{
  Bitmap bmp = new Bitmap(ctl.ClientRectangle.Width, ctl.ClientRectangle.Height);
  System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmp);
  g.CompositingMode = CompositingMode.SourceCopy;
  g.CopyFromScreen(ctl.PointToScreen(ctl.ClientRectangle.Location), new Point(0, 0), ctl.ClientRectangle.Size);
  return bmp;
}