image/sourced.go
func FromSource(ctx context.Context, sys *types.SystemContext, src types.ImageSource) (types.ImageCloser, error) {
	img, err := FromUnparsedImage(ctx, sys, UnparsedInstance(src, nil))
	if err != nil {
		return nil, err
	}
	return &imageCloser{
		Image: img,
		src:   src,
	}, nil
}
func FromSource(ctx context.Context, sys *types.SystemContext, src types.ImageSource) (types.ImageCloser, error) {
	img, err := FromUnparsedImage(ctx, sys, UnparsedInstance(src, nil))
	if err != nil {
		return nil, err
	}
	return &imageCloser{
		Image: img,
		src:   src,
	}, nil
}
// FromSource returns a types.ImageCloser implementation for the default instance of source.
// If source is a manifest list, .Manifest() still returns the manifest list,
// but other methods transparently return data from an appropriate image instance.
//
// The caller must call .Close() on the returned ImageCloser.
//
// FromSource “takes ownership” of the input ImageSource and will call src.Close()
// when the image is closed.  (This does not prevent callers from using both the
// Image and ImageSource objects simultaneously, but it means that they only need to
// the Image.)
//
// NOTE: If any kind of signature verification should happen, build an UnparsedImage from the value returned by NewImageSource,
// verify that UnparsedImage, and convert it into a real Image via image.FromUnparsedImage instead of calling this function.