There is no need to copy or transfer the docker image. Its contents, which is just the executable code for each container, are downloaded when a docker is installed or updated. What might be worthwhile transferring is the appdata for your dockers, and the templates for each. Probably you already know where the appdata is. The templates are on flash in config/plugins/dockerMan/templates-user. The templates contain the settings for each container, which is all those things you have to fill out when you create or edit a container, such as the mappings, etc.