In my readme on GitHub I have several images that are present there in my project's source tree which I reference successfully with directives like
.. image:: ./doc/source/_static/figs/moon_probe.png
I would also like to have these images appear when this same readme is generated in PyPi.
How do I (a) ensure that images are present on PyPi for the readme to access and (b) formulate the .. image:: directive to access them?
PyPI will not read your package distributions for the image. You have to use the image's external link, for example:
.. image:: https://raw.githubusercontent.com/greyli/flask-share/master/images/demo.png
If you are using Markdown description, use this:

Be sure to replace the URL in the above examples with your image URL, here I use the image hosted by GitHub, the real demo is on PyPI.
P.S. To get the image's raw link on GitHub, right-click the image and choose Copy image address.
Go to the image address in the Github repository. The path shown will be like this:
https://github.com/tensorbored/kds/blob/master/docs/_static/readme_lift.png
Change the blob term in the image address to raw
https://github.com/tensorbored/kds/raw/master/docs/_static/readme_lift.png

If you have your images on Github, navigate to the image then right click on download button and copy link address:
Then you can add it in your README.md file:

It should be rendered properly both on Github and PyPi.