blog/_src/_includes/picture.html

{% case include.size %}

{% when 'phototeaser' %}
     {% assign pictureSize = 'w_940%2Ch_700%2Cc_fill' %}
     {% assign pictureSizeRetina = 'w_1880%2Ch_1400%2Cc_fill' %}
{% when 'photothumb' %}
    {% assign pictureSize = 'w_190%2Ch_190%2Cc_thumb' %}
    {% assign pictureSizeRetina = 'w_380%2Ch_380%2Cc_thumb' %}
{% when 'featured' %}
    {% assign pictureSize = 'w_275%2Ch_100%2Cc_fill' %}
    {% assign pictureSizeRetina = 'w_550%2Ch_200%2Cc_fill' %}
{% else %}
     {% assign pictureSize = 'w_940' %}
     {% assign pictureSizeRetina = 'w_1880' %}
{% endcase %}

{% if include.file %}
    {% assign pictureSrc = include.file %}
{% else %}
    {% if page.image %}
        {% assign pictureSrc = page.image %}
    {% else %}
        {% assign pictureSrc = post.image %}
    {% endif %}
{% endif %}

<picture>
    <source srcset="{{ site.media_url }}/{{ pictureSizeRetina }}/media/{{ pictureSrc }}" media="(-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi)">
    <img srcset="{{ site.media_url }}/{{ pictureSize }}/media/{{ pictureSrc }}" alt="">
</picture>