* is called on the WIM once for each image, with each image selected as the
* current image in turn. If @image is a certain image, @visitor is called on
* the WIM only once, with that image selected.
* is called on the WIM once for each image, with each image selected as the
* current image in turn. If @image is a certain image, @visitor is called on
* the WIM only once, with that image selected.