So to fetch all the unused docker images without actually pruning them, you could do the following

1. Fetch all the images belonging to the running containers(which are not stopped or exited)
2. Fetch all the images on the machine
3. Then filter the images in step 1 from step 2

Below are the shell commands:

runningImages=$(docker ps --format {{.Image}})
docker images --format "{{.ID}} {{.Repository}}:{{.Tag}}" | grep -v "$runningImages"