Try going to Admin Zone > Style > Manage Themes > Edit theme images (default theme) first. That should make it do a scan and pick up any new directories.
Empty the block cache and any new directories will then appear as a field type. This is now documented.
Note that the root theme image directories will not show, it has to be a subdirectory. I don't want to encourage massive proliferation of images in the root theme image directory.
Note that the root theme image directories will not show, it has to be a subdirectory. I don't want to encourage massive proliferation of images in the root theme image directory.