add og:image:alt

src/_includes/layouts/default.njk

@@ -13,6 +13,7 @@
     <meta property="og:description" content="{{ description if description else site.description }}">
     <meta property="og:url" content="{{ site.url }}{{ page.url }}">
     <meta property="og:image" content="{% if feature_image %}{{ site.url }}{{ feature_image }}{% else %}{{ site.url }}/img/cover.jpg{% endif %}">
+    {% if feature_alt %}<meta property="og:image:alt" content="{{ feature_alt }}">{% endif %}
     <meta property="og:site_name" content="{{ site.title }}">
     <meta name="article:author" content="{{ site.name }}">
     {% if date %}<meta name="article:published_time" content="{{ date | date_to_datetime }}">{% endif %}