This variable was not defined for the view photo page. To add this variable, you should go to /ow_plugins/photo/controllers/photo.php file. Find the following string:
OW::getDocument()->setTitle($language->text('photo', 'meta_title_photo_view', array('title' => $description)));
and add the'displayName' => $displayName variable.
Also the $displayName variable should be describe in this function. So, you should add the following string:
$displayName = BOL_UserService::getInstance()->getDisplayName($userId);
Finally, the code should look the following way:
$description = strip_tags($photo->description);
$description = mb_strlen($description) ? $description : $photo->id;
$displayName = BOL_UserService::getInstance()->getDisplayName($userId);
OW::getDocument()->setTitle($language->text('photo', 'meta_title_photo_view', array('displayName' => $displayName, 'title' => $description)));
$tagsArr = BOL_TagService::getInstance()->findEntityTags($photo->id, 'photo');
I hope this example will help all developers who have the problems with the variables functionality.