Why does System.Drawing.Image.GetThumbnailImage require an unused delegate?

[princesh]

This blows my mind. Why does this method require an unused argument? Also, it requires an IntPtr that "Must be Zero." This seems to be entirely pointless. Can anyone explain?Docs here: http://msdn.microsoft.com/en-us/library/system.drawing.image.getthumbnailimage.aspx