I recently received a bug report about some huge container images not working correctly in Docker. So I suggested to the reporter that they try them with Podman. He responded that he saw the images with docker images, but did not see them with podman images.
I explained to him that the Docker image and container database are separate from the Podman image and container database. I told him he would have to pull the images into Podman. Then I decided to try a cool feature of Podman, where I could pull images directly out of the Docker daemon.
# docker images | grep centos docker.io/centos 7 49f7960eb7e4 2 months ago 200 MB
Podman has the ability through its use of containers/image to pull images using many different transports other than just pulling from Container Registries. It supports pulling directly from the Docker daemon, using the docker-daemon transport.
# podman pull docker-daemon:docker.io/centos:7 Getting image source signatures Copying blob sha256:bcc97fbfc9e1a709f0eb78c1da59caeb65f43dc32cd5deeb12b8c1784e5b8237 198.59 MB / 198.59 MB [====================================================] 1s Copying config sha256:49f7960eb7e4cb46f1a02c1f8174c6fac07ebf1eb6d8deffbcb5c695f1c9edd5 2.15 KB / 2.15 KB [========================================================] 0s Writing manifest to image destination Storing signatures 49f7960eb7e4cb46f1a02c1f8174c6fac07ebf1eb6d8deffbcb5c695f1c9edd5
Now you have the Centos 7 image in Podman containers/storage datastore.
#podman images | grep centos docker.io/library/centos 7 49f7960eb7e4 2 months ago .com208MB
Now you can start using the image with Podman, Buildah and CRI-O. You can even create new images and push them back into the Docker daemon.