Copyrighted content is not illegal. Anyway, in this case, the initial download of the otherwise redistributable content would be piracy. From the docker TOS:
> 2.4 You may not access or use the Service for the purpose of bringing an intellectual property infringement claim against Docker or for the purpose of creating a product or service competitive with the Service.
Which is a great reason to default to / publish on other registries.
> 2.4 You may not access or use the Service for the purpose of bringing an intellectual property infringement claim against Docker or for the purpose of creating a product or service competitive with the Service.
Which is a great reason to default to / publish on other registries.