Docker images are the building blocks of a Docker container, and they are stored in a Docker registry. A Docker registry is a centralized service for storing and distributing Docker images. The most popular and widely used registry is the Docker Hub, but there are also other registries available such as the Google Container Registry and the Amazon Elastic Container Registry.When you run a command to pull an image from a registry, the image is stored locally on your machine in the Docker daemon's storage area. The Docker daemon manages the images and their storage on the host machine. Each image is stored as a series of layers, with each layer representing a change made to the image. This allows for efficient storage and distribution of images, as only the layers that have changed need to be downloaded when pulling an updated version of an image.In addition to the Docker Hub, you can also create and run your own private registries. This allows you to store and distribute images within your organization, without making them publicly available. You can use the Docker Registry API to create, manage, and distribute your own images.It's also possible to store images on other storage solutions, such as NFS, S3, and GlusterFS. This can be useful in cases where you need to share images between multiple hosts or need to store images in a centralized location.In conclusion, Docker images are the building blocks of a Docker container and they are stored in a Docker registry. The most popular and widely used registry is the Docker Hub, but there are also other registries available such as the Google Container Registry and the Amazon Elastic Container Registry. The images are stored locally on the machine in the Docker daemon's storage area and are distributed in a series of layers. It's also possible to store images on other storage solutions, such as NFS, S3, and GlusterFS, and to create and run your own private registries.