Creating custom Docker images for testing purposes is now straightforward using TestContainers. The GenericContainer class accepts a Future as an argument, which allows the image to be created asynchronously. This can be achieved by utilizing the ImageFromDockerfile class, which takes a Dockerfile and other necessary files from the classpath, allowing developers to build their own custom images just before running tests. Additionally, exposed ports are easily specified, and the waitingFor method ensures that the container is ready for testing. It's also possible to keep the images even after test completion by passing a flag.