==== Mount a .gz compressed image file using nbdkit and nbd-client (read-only) ====

<code bash>
# create the server that decompresses the file live
nbdkit -i 127.0.0.1 /usr/lib/(your-machine-arch)/nbdkit/plugins/nbdkit-gzip-plugin.so file=test.img.gz
# connect to the server and create a device interface on /dev/nbd0
nbd-client 127.0.0.1 10809 /dev/nbd0

# once finished, you can clean-up everything by:
nbd-client --disconnect /dev/nbd0
pkill nbdkit
</code>

Source: https://askubuntu.com/questions/836217/how-to-mount-a-compressed-disk-image