C#: How do you implement the proxy pattern?

1public interface IImage
2{
3    void Display();
4}
5
6public class RealImage : IImage
7{
8    public void Display() => Console.WriteLine("Displaying image");
9}
10
11public class ProxyImage : IImage
12{
13    private RealImage _real;
14    private readonly string _filename;
15
16    public ProxyImage(string filename) => _filename = filename;
17
18    public void Display()
19    {
20        if (_real == null)
21            _real = new RealImage();
22        _real.Display();
23    }
24}