erynwells.me/layouts/shortcodes/photo.html

{{- with $photoPage := $.Page.GetPage (printf "photos/%s" (.Get 0)) -}}
  {{- $thumbnail := partial "photos/thumbnail.html" (dict "Page" . "Width" 1280 "Height" 1280) -}}
  {{- $altText := $thumbnail.Params.alt | default .Title -}}
  <a class="to-photo-post" href="{{ .RelPermalink }}" title="{{ .Title }}">
    <img src="{{ $thumbnail.RelPermalink }}"{{ with $altText }} alt="{{ . }}"{{ end }}>
  </a>
{{- else -}}
  {{- errorf "No page matching '%s'" (.Get 0) -}}
{{- end -}}