blog/_src/_includes/relatedphotos.html

<aside class="related-photos">

    <div class="grid">

        {% for post in site.categories['photos'] limit:6 %}

            <article class="related-photo col3-xs col2">
                <a class="photo-link" href="{{ post.url }}">
                    {% picture photothumb {{ post.image }} %}
                </a>
            </article>

        {% endfor %}

    </div>

</aside>