My understanding is that all images associated with posts are preserved in the Nabble archive.
To import the archive into another non-Nabble forum will require an appropriate script to do the job. I'm afraid you are rather on your own with that. It is possible to developers of the board you wish to import it into will have the necessary skills and will be prepared to write the necessary script.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.