support providing a metadata file

layouts/partials/lightbox.html

@@ -4,7 +4,12 @@
   {{- range $i, $img := $imgs }}
   <div class="snap-lightbox-inner">
     <div class="numbertext">{{ add $i 1 }} / {{ len $imgs }}</div>
-    <img src="{{ $img }}" style="width:100%">
+    <img
+      src="{{ relURL $img.src }}"
+      {{ range $attr, $value := $img.html -}}
+        {{ safeHTMLAttr $attr }}={{ $value }}
+      {{ end -}}
+    />
   </div>
   {{- end -}}