Create a Json-like dictionary for image group. Extends the basic
        object with an array of image identifiers.

        Parameters
        ----------
        img_coll : ImageGroupHandle

        Returns
        -------
        (JSON)
            Json-like object, i.e., dictionary.

def to_dict(self, img_coll):
        """Create a Json-like dictionary for image group. Extends the basic
        object with an array of image identifiers.

        Parameters
        ----------
        img_coll : ImageGroupHandle

        Returns
        -------
        (JSON)
            Json-like object, i.e., dictionary.
        """
        # Get the basic Json object from the super class
        json_obj = super(DefaultImageGroupManager, self).to_dict(img_coll)
        # Add list of images as Json array
        images = []
        for img_group in img_coll.images:
            images.append({
                'identifier' : img_group.identifier,
                'folder' : img_group.folder,
                'name' : img_group.name
            })
        json_obj['images'] = images
        # Transform dictionary of options into list of elements, one per typed
        # attribute in the options set.
        json_obj['options'] = attribute.attributes_to_dict(img_coll.options)
        return json_obj