Grid grid = new Grid();
grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });

Image image1 = new Image { Source = "image1.jpg" };
Grid.SetColumn(image1, 0);
grid.Children.Add(image1);

Image image2 = new Image { Source = "image2.jpg" };
Grid.SetColumn(image2, 1);
grid.Children.Add(image2);

Image image3 = new Image { Source = "image3.jpg" };
Grid.SetColumn(image3, 2);
grid.Children.Add(image3);