How to I associate an image with a instance of my class

Usually there are many methods of creating an image. In .NET you can use a Bitmap to create an image on the run-time too. So it is not a problem creating the images in .NET, on the run-time too.

If you're using Windows Forms, then use System.Drawing.Bitmap[^], or if you're using the WPF application, use the System.Windows.Media.Imaging.BitmapImage[^]

But a better way would be since you're going to have a defined image (either green or red, or any other particular color) in your application, then create a simple either R, G, B image and add it to your project and use it along with your class.

One more thing, you can add this Image field to your Robot class too. Like this,

public class Robot {
   // other properties, you can set it as a private one too
   public Image RobotImage { get; set; }

   // program logic and methods
}

Now each time you will create a Robot (object) you will be able to set the Image it would have for itself. This way, you won't need to do any other coding, it will be set as a property for the Robot.