Default to responsive lazyloaded images

post.hbs

@@ -13,7 +13,16 @@
         {{/if}}
 
         {{#if feature_image}}
-            <img class="gh-feature-image" src="{{feature_image}}" alt="{{title}}" />
+        <img class="gh-feature-image"
+            srcset="{{img_url feature_image size="s"}} 300w,
+                    {{img_url feature_image size="m"}} 600w,
+                    {{img_url feature_image size="l"}} 1000w,
+                    {{img_url feature_image size="xl"}} 2000w"
+            sizes="(max-width: 1000px) 400px, 700px"
+            loading="lazy"
+            src="{{img_url feature_image size="m"}}"
+            alt="{{title}}"
+        />
         {{/if}}
     </header>
 
@@ -50,4 +59,4 @@
     </div>
 </aside>
 
-{{/post}}
+{{/post}}