The latter. You or an attacker could tamper with the images - however even with the Dockerfiles I can't be sure that the provided images are built from the Dockerfiles, so in the end I'd have to trust you anyway. Also I'd be curious how you build the images.
Thanks for your answer!
Your feedback about Dockerfiles is good though and probably something we can easily add to image listings. I opened an issue for us to add.
Note that we also make our package manager freely available in Community Edition as well, which can make the Dockerfile availability more useful.