public Geometry Shape {get; set;}

// get the current mapview
var mapView = MapView.Active;
if (mapView == null)
  return;

      // 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);