When GetSource is called, the progress event is automatically raised with value '0', and when the image is returned, the progress event is again raised with value 100. Raise the progress event to fire progress events in between 0 and 100, for instance to report the progress of a download, image generation etc.

If the returned image from GetSource is a System.Windows.Media.Imaging.BitmapImage with a URL source, the progress event is automatically tracked, and there is no need to raise the progress event.