or the image handling in plantuml and graphviz we need access via the API in read mode
So if a local image is mentioned we need to get access to it which in the past could be done like in https://www.mediawiki.org/wiki/Topic:Pzvu1613ewnfahcd
For storing images it would be good to allow different methods of reference:
by name / version
by crc32 code
and then it should not make much of a difference whether a local or remote service delivers the result. This would give us quite some flexibility. I find it interesting that there are so many extensions with similar issues:
the extensions have in common that the input is some markup and the output a graphical representation - in case of the 3D extensions even in an interactive manner - and that some external software is needed for rendering.