When reading/writing a disk image using Linux tool ‘dd’ launch as follows:
dd if=/dev/sdb of=filename.img & pid=$!
this will run ‘dd’ in the background.

To see the progress:
kill -USR1 $pid
(it will not kill the dd)

Notes:

1. If you are doing it as a non-root user you’ll need to prefix those commands with sudo
2. If you do that do ‘sudo ls‘ first, otherwise the ‘sudo dd‘ will fail waiting on the password which it’ll never get as its backgrounded.

Thanks to Cian.