QUESTION:
Why aren't we taking an image of the Probe as it drifts away from
the Orbiter after separation? 

ANSWER from FAQ:
Imaging the Probe as it drifts away from the Orbiter was
contemplated both for engineering assessment (that is, looking for
any problems with the Probe hardware) and optical navigation. In
order to assess the external condition of the Probe, detailed pictures
would be desireable, but, because the SSI is focused on infinity,
objects up close would be out of focus. In fact, by the time the
Probe is in focus (at about 18 km away from the Orbiter), it would
only be about 2-3 resolution elements (about 4-6 pixels)
across--not very detailed! 

Taking a picture of the Probe for Optical Navigation purposes
appears to be feasible , but, because the Probe delivery knowledge
requirements are being met, and because of the operational costs of
trying to return large data sets (such as images), it was decided not
to pursue optical navigation.