What are the licenses governing the distribution of a container? Answering this question has led me on a journey into Dockerfile patterns, container image metadata, container OSes and linux filesystems . The result of my work is an open source project called Tern which inspects container images for packages installed in them along with their associated metadata for Open Source Software compliance. In this talk, I will go through how container images are built, what their metadata look like, and how you can figure out what is installed in them.