In order to keep our images up to date for the security patches, we need to know from which base image we depend

How to find from which image our image comes from

As an example, lets us look at a Wordpress container

The Dockerfile begins with FROM php:5.6-apache

so we go to the Dockerfile abovementioned

and we find FROM debian:jessie So this means that we a security patch appears for Debian jessie, we need to build again our image.