Here i am trying to create docker image from ubuntu 14.04 ISO file, knowing ubuntu 14.04 is already available in docker hub. Because later i have to create docker images for
You're building an image from ubuntu's iso but what you really want is building an image from an ubuntu install.
What you have to do is :
install ubuntu from the iso inside a VM
make an archive or the VM's /
import with docker
I hope that helps