These images are heavy influenced by SeleniumHQ docker images. However, there are some differences.
The base image for the SeleniumHQ images are ubuntu:16.04 and have selenium-server installed. We have based our images on python:3.7.0-stretch and do not have selenium-server installed. At this current time we run the tests locally so do not need to run a remote webdriver.
We also like to keep our Python version up-to-date as possible, hence the use of Python 3.7. The use of Debian stretch/jessie is consistent with other docker builds utilized by other OpenStax teams.
The SeleniumHQ docker build files are licensed under APLv2 which is included in our license file.