public string PictureURL {get; set;}

{
  // Use SourceURL for the URL to the image content. For
  // a local file, use a file path. For a web/internet file
  // location, use its URL
  //
  // Supported image types are:
  // png, jpg, tiff, bmp, gif, svg

  var pictureGraphic = new CIMPictureGraphic
  {
    SourceURL = @"C:\Images\MyImage.png",
    Shape = envelope
  };

  IDisposable _graphic = mapView.AddOverlay(pictureGraphic);
}