WPF Image Image.Source DrawingImage DrawingGroup ImageDrawing

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp57
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            InitImageDrawingGroup();
        }

        private void InitImageDrawingGroup()
        {
            DrawingGroup drawingGroup = new DrawingGroup();
            ImageDrawing firstImg = new ImageDrawing();
            firstImg.Rect = new Rect(0, 0, 400, 400);
            firstImg.ImageSource = new BitmapImage(new Uri(@"../../Images/1.jpg", UriKind.RelativeOrAbsolute));
            drawingGroup.Children.Add(firstImg);

            ImageDrawing secondImg = new ImageDrawing();
            secondImg.Rect = new Rect(400, 0, 400, 400);
            secondImg.ImageSource = new BitmapImage(new Uri(@"../../Images/2.jpg", UriKind.RelativeOrAbsolute));
            drawingGroup.Children.Add(secondImg);

            ImageDrawing thirdImg = new ImageDrawing();
            thirdImg.Rect = new Rect(0, 400, 800, 800);
            thirdImg.ImageSource = new BitmapImage(new Uri(@"../../Images/3.jpg", UriKind.RelativeOrAbsolute));
            drawingGroup.Children.Add(thirdImg);

            ImageDrawing forthImg = new ImageDrawing();
            forthImg.Rect = new Rect(800, 0, 800, 800);
            forthImg.ImageSource = new BitmapImage(new Uri(@"../../Images/4.jpg", UriKind.RelativeOrAbsolute));
            drawingGroup.Children.Add(forthImg);

            DrawingImage drawImgSource = new DrawingImage(drawingGroup);
            drawImgSource.Freeze();
            Image imgControl = new Image();
            imgControl.Stretch = Stretch.None;
            imgControl.Source = drawImgSource;

            Border imgBorder = new Border();
            imgBorder.BorderBrush = Brushes.Black;
            imgBorder.BorderThickness = new Thickness(10);
            imgBorder.HorizontalAlignment = HorizontalAlignment.Stretch;
            imgBorder.VerticalAlignment = VerticalAlignment.Stretch;
            imgBorder.Child = imgControl;

            this.Background = Brushes.White;
            this.Margin = new Thickness(10);
            this.Content = imgBorder;
        }
    }
}