Huh? I mean, sure, you can probably figure out the _names_ of the environment variables expected by the code of the image, but the image itself doesn't have the values for those variables.

Environment files are—unless I'm missing something—a run-time consideration. You provide the an env-file you have locally to connect to your development images, etc., and could deploy (possibly) the same image elsewhere, with a different env-file. But the env-file values are not baked into the image.