In addition to the post from Josh Odgers it seems it is not well known how to upload an ISO/Image directly from a NFS share to the image service. To achieve this you can leverage the “From URL” field in the PRISM interface.

The format for anonymous nfs access is:

nfs://IP-or-DNS/share/subfolders/isofilename

If user and password is required:

nfs://user:password@IP-or-DNS/share/subfolders/isofilename

Example: