including images in html output

It seems, that including images in the final document (i.e. html) is currently only possible, if the images are directly located in the source folder. Having them in a folder relative to source, e.g. $source/images, will result in a build error telling:

FileNotFoundError: [Errno 2] No such file or directory: 'document_data/images/pid_overview.drawio.png'

Instead, for pdf outputs it is working also with relative paths.