I haven't really worked with WPF so this is a bit of a guess. I read the documentation for the BitmapImage class and it says that it exists mainly to extend the BitmapSource class for use in XAML. As you're not using it in XAML, maybe try creating a BitmapSource instead and see if the same problem occurs. If it does then I would say that your only option would be to create the object on the UI thread if you intend to display it in the UI.