k3d/docs/usage/importing_images.md

Importing modes

Auto

Auto-determine whether to use direct or tools-node.

For remote container runtimes, tools-node is faster due to less network overhead, thus it is automatically selected for remote runtimes.

Otherwise direct is used.

Direct

Directly load the given images to the k3s nodes. No separate container is spawned, no intermediate files are written.

Tools Node

Start a k3d-tools container in the container runtime, copy images to that runtime, then load the images to k3s nodes from there.