Index: src/routes/posts.js
===================================================================
--- src/routes/posts.js	(revision 3a2c9d3bd2a16914b0e05ace0ec9a4b522932dd6)
+++ src/routes/posts.js	(revision 52ea6df4abea1a346a912f9f11d8e52a474df932)
@@ -753,4 +753,6 @@
   // Owner/admin of this site may reply back to a fediverse interaction.
   const canManageSite = !!(req.session?.user && PermissionsService.canAdminSite(req.session.user, site));
+  // Avatar for our own (outbound) fediverse replies = the site's profile photo.
+  const siteAvatar = (site && site.profile_photo) ? site.profile_photo : null;
 
   renderPage(req, res, 'pages/post', {
@@ -763,4 +765,5 @@
     fediverse,
     canManageSite,
+    siteAvatar,
     likeCount,
     likedByMe,
Index: src/views/pages/post.ejs
===================================================================
--- src/views/pages/post.ejs	(revision 3a2c9d3bd2a16914b0e05ace0ec9a4b522932dd6)
+++ src/views/pages/post.ejs	(revision 52ea6df4abea1a346a912f9f11d8e52a474df932)
@@ -116,5 +116,8 @@
                     <% mine.forEach(function(o){ %>
                       <li class="comment comment-reply">
-                        <div class="comment-avatar"><span><%= t('fedi.you').charAt(0).toUpperCase() %></span></div>
+                        <div class="comment-avatar">
+                          <% if (typeof siteAvatar !== 'undefined' && siteAvatar) { %><img src="<%= siteAvatar %>" alt="">
+                          <% } else { %><span><%= t('fedi.you').charAt(0).toUpperCase() %></span><% } %>
+                        </div>
                         <div class="comment-body">
                           <div class="comment-meta"><span class="comment-author"><%= t('fedi.you') %></span></div>