https://github.com/NodeBB/NodeBB/issues/3530

templates/partials/chat_message.tpl

@@ -1,6 +1,6 @@
 				<li class="chat-message clear" data-uid="{messages.fromuid}" data-self="{messages.self}" data-break="{messages.newSet}">
 					<div class="message-header">
-						<a href="{config.relative_path}/user/{messages.fromUser.userslug}"><img class="chat-user-image img-circle" src="{messages.fromUser.picture}"></a>
+						<a href="{config.relative_path}/user/{messages.fromUser.userslug}"><img class="chat-user-image img-circle not-responsive" src="{messages.fromUser.picture}"></a>
 						<strong><span class="chat-user">{messages.fromUser.username}</span></strong>
 						<span class="chat-timestamp timeago" title="{messages.timestampISO}"></span>
 					</div>