I found that the Pelican site theme I was using was automatically expanding images to 100% width, which I didn’t want to have. I also wanted to use captions on my images.
Thanks to Joe Lotz I was able to sort this out.
python -m pip install pandoc
python -m pip install pelican-pandoc-reader
pip freeze > requirements.txt
NEST_CSS_MINIFY = True to
NEST_CSS_MINIFY = False; without this change the minified css file is used instead and my custom css is ignored.
width: 100% and
height: 100% from nest.css, and add the captioning CSS that I wanted to use to lazaruk.css.
This also served as a good reminder that css settings for images override the settings on individual images. Because I wanted to use the individual settings to define image size I needed comment those out of the css completely.