If it’s an open-source project, usually the dockerfiles are available for reading.

Do you audit every line of code that you run in production? If you are trying some new python/django/sql app, are you reviewing all that?

I’d assume with a python based project, you’d be able to at least look at requirements and tell there’s something that sets off red flags. And you are either familiar/trust the maintainer, or you are reviewing the actual python itself?

Beyond that, the dockerfile is essentially just installation instructions for getting it running on a virgin system of X distribution. I wouldn’t call that a black box.

If the container isn’t part of an open source project, then this is a moot point then. The project itself is a black box.