{% if include.author.email and include.author.use_picture != false %}
  {% assign use_picture = include.author.use_picture | default: "gravatar" %}
  <span class="author-avatar">
    {% if use_picture == "gravatar" %}
      {% assign author_pic_url = "https://gravatar.com/avatar/" | append: include.author.email | append: "?s=64" %}
    {% elsif use_picture == "assets" %}
      {% assign author_pic_url = "/assets/blog/authors/" | append: include.author.plaintext_email | append: ".jpg" %}
    {% else %}
      {% assign author_pic_url = "/assets" | append: use_picture %}
    {% endif %}
    <img src="{{ author_pic_url | relative_url }}" alt="Author’s picture">
  </span>
{% endif %}