It looks like RST does not create [Illustration] tags in plain text files.  For instance, I use this:

.. image:: images/bhagap011.png
   :alt: A diagram of concentric circles with P at the center and M' the outermost, with the Key below working inwards.

hoping to get this in my plain text file:

[Illustration: A diagram of concentric circles with P at the center and M' the outermost, with the Key below working inwards.]

but instead I get no [Illustration] tag at all.

James Simmons