How to make graphics overlap in a StackPanel or other container

I have a StackPanel in which I wish to place images that are 100 x 100 pixels, in a vertical orientation.  One of the images is is a bit taller than 100 pixels, it's about 140.  A portion of the top 20 pixels and bottom 20 pixels of the image are transparent.  I wish to add that image into the StackPanel, along with the other images, such that the non-transparent portions at the top of the image overlap the images that are above and below it in the StackPanel.  

Can this be achieved?   I am using code similar to below to add an image to the StackPanel:

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            var bitmap = new BitmapImage();
            bitmap.BeginInit();
            bitmap.UriSource = new Uri(@"C:\SomeFolder\Images\image.png");
            bitmap.DecodePixelWidth = 100;
            bitmap.EndInit();
            UIElement image = new Image { Source = bitmap, Margin = new Thickness(0), Stretch = Stretch.None };
            StackPanel1.Children.Add(image);
        }