Setting up Docker Registry is only required if you plan to run your Captain on a cluster. For single node Captain deployments, Docker Registry is optional. Captain provides two methods for you to setup your docker registry:

• Self hosted Docker Registry: This is the simplest way to setup a docker registry. Captain creates an instance of Docker Registry on the main machine and it manages the registry for you. However, it has its own limitation. If your main machine is destroyed, your local images will be lost. In most cases, this is not a disaster as you can re-deploy your apps from your source code.
• Remote Docker Registry: This approach relies on a remote service to act as your Docker Registry. Using this approach, you'll have a more reliable cluster, assuming the third party service you use is reliable! There are multiple private Docker Registry services available: Google Container Registry, Amazon EC2 Container Registry, Quay and etc. Note that this approach costs you money.

You can switch between the two approaches, but you'll have to re-deploy your apps to Captain again such that your images get created on your new Docker Registry. Unless you lost access to the source code, this is a relatively easy task.