Hmmm, unless it changed recently, images from private repos can only be pulled by authenticated users. At least it was the case with Tutum and Amazon ECR, and I'd be very surprised that it's not the case with Dockerhub (will give it a try later, removing my credentials and trying to pull an image, but I'm very confident that private images are private, and that's precisely why you have to correctly setup your credentials (or fill your .dockercfg file) to be able to get them.