private void InitRows(int rowCount,Grid g)
        {
            while (rowCount-- > 0)
            {
                RowDefinition rd = new RowDefinition();
                rd.Height = new GridLength();
                g.RowDefinitions.Add(rd);
            }
        }
  private void InitColumns(int colCount, Grid g)
        {
            while (colCount-- > 0)
            {
                ColumnDefinition rd = new ColumnDefinition();
                rd.Width = new GridLength();
                g.ColumnDefinitions.Add(rd);
            }
        }

 private void Init(Grid g)
        {
            InitRows(5, g);
            InitColumns(5, g);
            for (int r = 0; r < 5; r++)
            {
                for (int c = 0; c < 5; c++)
                {
                    Image img = new Image();
                    g.Children.Add(img);
                    Grid.SetColumn(img, c);
                    Grid.SetRow(img, r);
                }
            }
        }

for (int i = 0; i < 5; i++)
{
    LayoutRoot.ColumnDefinitions.Add(
        new ColumnDefinition());  // *
        //new ColumnDefinition() { Width = GridLength.Auto }); // Auto
        //new ColumnDefinition() { Width = new GridLength(double.NaN, GridUnitType.Star) }); *
        //new ColumnDefinition() { Width = new GridLength(0.1, GridUnitType.Star) }); // 0.1*
        //new ColumnDefinition() { Width = new GridLength(100) }); // 100
}

for (int i = 0; i < 5; i++)
{
    LayoutRoot.RowDefinitions.Add(
        new RowDefinition());  // *
}

LayoutRoot.ShowGridLines = true;

// create a image
GeometryGroup ellipses = new GeometryGroup();
ellipses.Children.Add(new EllipseGeometry(new Point(40, 40), 20, 30));
ellipses.Children.Add(new EllipseGeometry(new Point(40, 40), 30, 20));

GeometryDrawing geo = new GeometryDrawing();
geo.Geometry = ellipses;
geo.Brush = Brushes.Brown;
geo.Pen = new Pen(Brushes.Black, 2);
DrawingImage image = new DrawingImage(geo);
image.Freeze();

Image[,] images = new Image[5, 5];

for (int row = 0; row < 5; row++)
{
    for (int col = 0; col < 5; col++)
    {
        images[col, row] = new Image();
        images[col, row].Source = image;
        images[col, row].SetValue(Grid.ColumnProperty, col);
        images[col, row].SetValue(Grid.RowProperty, row);
        LayoutRoot.Children.Add(images[col, row]);
    }
}