Added og:image url for OpenGraph data (thanks to anonymous user on DokuWiki

helper.php

@@ -280,6 +280,7 @@ class helper_plugin_semantic extends DokuWiki_Plugin {
       'og:description' => str_replace("\n", ' ', $this->getDescription()),
       'og:url'         => wl($this->page, '', true),
       'og:type'        => 'website',
+      'og:image'       => $this->getFirstImageURL(),
     );
 
     return $open_graph;

plugin.info.txt

@@ -1,7 +1,7 @@
 base semantic
 author Giuseppe Di Terlizzi
 email giuseppe.diterlizzi@gmail.com
-date 2016-12-12
+date 2017-05-23
 name Semantic Plugin
 desc Add Semantic Data in DokuWiki
 url http://www.dokuwiki.org/plugin:semantic