Would like an upload tool

I have a large markdown database using Joplin, and would like to upload notes into HedgeDoc so that I can share them more easily. In particular, I have a note in Joplin with several images that I would like to share with HedgeDoc. The Joplin md format is fully compatible, and Joplin has a host of export options, both for individual notes and entire notebooks.
Its impractical to export every image individually out of a jopilin note, copy in the markdown text, and then reinsert each image.
I would like an upload feature.

did you look at GitHub - hedgedoc/cli: A tiny CLI for HedgeDoc?
The CLI allows you to import notes from your local filesystem.

To upload images, HedgeDoc does a POST to https://<your_hedgedoc_domain>/uploadimage.
This returns: {“link”:“https://<your_hedgedoc_domain>/uploads/filename.ext”}

You could probably write a simple script to upload all media, replace all references to these images in your markdown via regexp, then import the markdown into HedgeDoc using the CLI.