Autosort a Category by posts Featured Image Title
The Automatic Order functionality along with Custom Function it’s a very powerful tool to customize the sort of a give area by very specific criteria. As specified at https://www.nsp-code.com/applying-automatic-order-for-a-sort-through-a-user-function-callback/ the filter return a list of all posts within the section / query on which different operations can apply.
In the following example, a sort list is ordered by the posts Featured Images Title. After creating a simple sort as show at https://www.nsp-code.com/advanced-post-types-order-description-and-usage/ chose Automatic Order, then Custom Function. As parameter, use function name which should be included within theme functions.php or a custom plugin, in this example custom_sorting_function_featured_file
function custom_sorting_function_featured_file($post_list, $sort_view_id, $orderBy, $query)
{
$list_map_feature = array();
foreach($post_list as $object_id)
{
$thumbnail_id = get_post_meta($object_id, '_thumbnail_id', TRUE);
if(empty($thumbnail_id))
continue;
$feature_post = get_post($thumbnail_id);
$list_map_feature[basename($feature_post->guid)] = $object_id;
}
//sort the dates ascending
ksort($list_map_feature);
$post_list = array_values($list_map_feature);
return $post_list;
}