root@iZ28krk4xlkZ:/var/lib# docker rm `docker ps -a -q`
958e1b65cde0
f4997df56049
4c258585a82c
3e4021f0b9e6
79537a175735
95751e6b23bf
root@iZ28krk4xlkZ:/var/lib# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
swarm latest eb7c36c2df64 18 hours ago 17.15 MB
rethinkdb latest 53c589ee884f 26 hours ago 181.8 MB
alpine latest 2314ad3eeb90 2 weeks ago 4.794 MB
shipyard/docker-proxy latest 276373c72857 5 weeks ago 9.468 MB
shipyard/shipyard latest 4db14669ff0c 8 weeks ago 58.73 MB
ehazlett/curl latest b26cc0beea49 5 months ago 8.751 MB
microbox/etcd latest 96192a5fe39d 5 months ago 17.87 MB
They have all been deleted. Why do you still have the mirror?
What you delete is the instance where the image is running. To delete the image, use docker rmi+image name or that string of characters.