Earlier quoted context omitted.
You'd think, but no, that's not actually how it's done. See e.g.: http://dnc.tamu.edu/drjunkins/yearwise/2000/conference/AIAA_... https://core.ac.uk/download/pdf/9069467.pdf for some state-of-the-art research on this topic.
Actually, in the case of New Horizons, it is. Mission navigators use LORRI images of known objects relative to the background stars to calibrate their position.
OK, I stand corrected.