For a client project I grabbed code from
as suggested in the post Extracting base64 encoded images from HTML - #2 by fredvd
On ObjectModifiedEvent my hacked monstrosity creates an image in the content item (it must be folderish) then changes the img tag src to be the newly created image, prepends the parent item ID to the path of the image, and uses a scaled version of the image.
I’m sure my code can be improved on, but at least now my users can quickly paste an image into what they’re writing and have Plone just do its expected thing.
I’ll see if I can pull out just that feature…