diff --git a/src/app/bots/page.tsx b/src/app/bots/page.tsx
index 9042ef5..0def9f4 100644
--- a/src/app/bots/page.tsx
+++ b/src/app/bots/page.tsx
@@ -13,6 +13,7 @@ import { useRouter } from 'next/navigation';
 import Link from 'next/link';
 import { ArrowLeftIcon } from '@/components/Icons';
 import { Bot, Plus, Sparkles } from 'lucide-react';
+import { AvatarImage } from '@/components/AvatarImage';
 
 interface BotData {
   id: string;
@@ -126,11 +127,7 @@ export default function BotsPage() {
                         fontSize: '18px',
                       }}
                     >
-                      {bot.avatarUrl ? (
-                        <img src={bot.avatarUrl} alt={bot.name} style={{ width: '100%', height: '100%', objectFit: 'cover', borderRadius: '50%' }} />
-                      ) : (
-                        bot.name.charAt(0).toUpperCase()
-                      )}
+                      <AvatarImage avatarUrl={bot.avatarUrl} seed={bot.handle} alt={bot.name} />
                     </Link>
                     <div style={{ flex: 1, minWidth: 0 }}>
                       <div style={{ display: 'flex', alignItems: 'center', gap: '8px', marginBottom: '4px' }}>
diff --git a/src/app/chat/page.tsx b/src/app/chat/page.tsx
index a98b741..618d815 100644
--- a/src/app/chat/page.tsx
+++ b/src/app/chat/page.tsx
@@ -7,6 +7,7 @@ import { ArrowLeft, Send, Loader2, MessageCircle, Search, Plus, Trash2, MoreVert
 import Link from 'next/link';
 import { getProfilePath, useFormattedHandle } from '@/lib/utils/handle';
 import { useRouter, useSearchParams } from 'next/navigation';
+import { AvatarImage } from '@/components/AvatarImage';
 
 interface Conversation {
     id: string;
@@ -386,11 +387,11 @@ export default function ChatPage() {
                             <ArrowLeft size={20} />
                         </button>
                         <div className="avatar" style={{ width: '32px', height: '32px', fontSize: '14px' }}>
-                            {selectedConversation.participant2.avatarUrl ? (
-                                <img src={selectedConversation.participant2.avatarUrl} alt="" />
-                            ) : (
-                                selectedConversation.participant2.displayName[0] || '?'
-                            )}
+                            <AvatarImage
+                                avatarUrl={selectedConversation.participant2.avatarUrl}
+                                seed={selectedConversation.participant2.handle}
+                                alt={selectedConversation.participant2.displayName || selectedConversation.participant2.handle}
+                            />
                         </div>
                         <div style={{ flex: 1, minWidth: 0 }}>
                             <Link
@@ -439,11 +440,11 @@ export default function ChatPage() {
                                 flexDirection: msg.isSentByMe ? 'row-reverse' : 'row'
                             }}>
                                 <div className="avatar avatar-sm" style={{ flexShrink: 0 }}>
-                                    {msg.isSentByMe ? (
-                                        user.avatarUrl ? <img src={user.avatarUrl} alt="" /> : user.displayName[0]
-                                    ) : (
-                                        msg.senderAvatarUrl ? <img src={msg.senderAvatarUrl} alt="" /> : msg.senderDisplayName?.[0]
-                                    )}
+                                    <AvatarImage
+                                        avatarUrl={msg.isSentByMe ? user.avatarUrl : msg.senderAvatarUrl}
+                                        seed={msg.isSentByMe ? user.handle : msg.senderHandle}
+                                        alt={msg.isSentByMe ? user.displayName : msg.senderDisplayName || msg.senderHandle}
+                                    />
                                 </div>
 
                                 <div style={{ display: 'flex', flexDirection: 'column', alignItems: msg.isSentByMe ? 'flex-end' : 'flex-start' }}>
@@ -595,7 +596,11 @@ export default function ChatPage() {
                             style={{ cursor: 'pointer', display: 'flex', alignItems: 'flex-start', gap: '12px' }}
                         >
                             <div className="avatar">
-                                {conv.participant2.avatarUrl ? <img src={conv.participant2.avatarUrl} alt="" /> : conv.participant2.displayName?.[0] || '?'}
+                                <AvatarImage
+                                    avatarUrl={conv.participant2.avatarUrl}
+                                    seed={conv.participant2.handle}
+                                    alt={conv.participant2.displayName || conv.participant2.handle}
+                                />
                             </div>
                             <div style={{ flex: 1, minWidth: 0 }}>
                                 <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'baseline' }}>
diff --git a/src/app/explore/page.tsx b/src/app/explore/page.tsx
index 7399239..c571a52 100644
--- a/src/app/explore/page.tsx
+++ b/src/app/explore/page.tsx
@@ -9,6 +9,7 @@ import { useFormattedHandle } from '@/lib/utils/handle';
 import { Bot, Network, Server, EyeOff } from 'lucide-react';
 import { useAuth } from '@/lib/contexts/AuthContext';
 import { signedAPI } from '@/lib/api/signed-fetch';
+import { AvatarImage } from '@/components/AvatarImage';
 
 interface User {
     id: string;
@@ -26,11 +27,7 @@ function UserCard({ user }: { user: User }) {
     return (
         <Link href={`/u/${user.handle}`} className="user-card">
             <div className="avatar">
-                {user.avatarUrl ? (
-                    <img src={user.avatarUrl} alt={user.displayName} />
-                ) : (
-                    user.displayName?.charAt(0).toUpperCase() || user.handle.charAt(0).toUpperCase()
-                )}
+                <AvatarImage avatarUrl={user.avatarUrl} seed={user.handle} alt={user.displayName || user.handle} />
             </div>
             <div className="user-card-info">
                 <div style={{ display: 'flex', alignItems: 'center', gap: '6px' }}>
diff --git a/src/app/notifications/page.tsx b/src/app/notifications/page.tsx
index 7ed071d..2583d82 100644
--- a/src/app/notifications/page.tsx
+++ b/src/app/notifications/page.tsx
@@ -5,6 +5,7 @@ import { BellIcon } from '@/components/Icons';
 import Link from 'next/link';
 import { useAuth } from '@/lib/contexts/AuthContext';
 import { getProfilePath } from '@/lib/utils/handle';
+import { AvatarImage } from '@/components/AvatarImage';
 
 interface NotificationActor {
     id: string;
@@ -218,32 +219,9 @@ function NotificationItem({
             }}
         >
             <Link href={actorProfilePath} style={{ flexShrink: 0 }}>
-                {actor?.avatarUrl ? (
-                    <img
-                        src={actor.avatarUrl}
-                        alt={actor.displayName || actor.handle}
-                        width={40}
-                        height={40}
-                        style={{ borderRadius: '50%', objectFit: 'cover' }}
-                    />
-                ) : (
-                    <div
-                        style={{
-                            width: 40,
-                            height: 40,
-                            borderRadius: '50%',
-                            background: 'var(--background-tertiary)',
-                            display: 'flex',
-                            alignItems: 'center',
-                            justifyContent: 'center',
-                            color: 'var(--foreground-secondary)',
-                            fontSize: '16px',
-                            fontWeight: 600,
-                        }}
-                    >
-                        {(actor?.displayName || actor?.handle || '?')[0].toUpperCase()}
-                    </div>
-                )}
+                <div className="avatar">
+                    <AvatarImage avatarUrl={actor?.avatarUrl} seed={actor?.handle || 'unknown'} alt={actor?.displayName || actor?.handle || 'Unknown user'} />
+                </div>
             </Link>
 
             <div style={{ flex: 1, minWidth: 0 }}>
diff --git a/src/app/search/page.tsx b/src/app/search/page.tsx
index b9be09f..f1e3714 100644
--- a/src/app/search/page.tsx
+++ b/src/app/search/page.tsx
@@ -9,6 +9,7 @@ import { Post } from '@/lib/types';
 import { Bot } from 'lucide-react';
 import { useAuth } from '@/lib/contexts/AuthContext';
 import { signedAPI } from '@/lib/api/signed-fetch';
+import { AvatarImage } from '@/components/AvatarImage';
 
 interface User {
     id: string;
@@ -82,11 +83,7 @@ function UserCard({ user }: { user: User }) {
             className="hover-bg"
         >
             <div className="avatar">
-                {user.avatarUrl ? (
-                    <img src={user.avatarUrl} alt={user.displayName} />
-                ) : (
-                    (user.displayName || user.handle).charAt(0).toUpperCase()
-                )}
+                <AvatarImage avatarUrl={user.avatarUrl} seed={user.handle} alt={user.displayName || user.handle} />
             </div>
             <div style={{ flex: 1, minWidth: 0 }}>
                 <div style={{ display: 'flex', alignItems: 'center', gap: '6px' }}>
diff --git a/src/app/settings/moderation/page.tsx b/src/app/settings/moderation/page.tsx
index bad2f1a..590844c 100644
--- a/src/app/settings/moderation/page.tsx
+++ b/src/app/settings/moderation/page.tsx
@@ -5,6 +5,7 @@ import Link from 'next/link';
 import { getProfilePath } from '@/lib/utils/handle';
 import { ArrowLeftIcon } from '@/components/Icons';
 import { UserX, Globe, Trash2 } from 'lucide-react';
+import { AvatarImage } from '@/components/AvatarImage';
 
 interface BlockedUser {
     id: string;
@@ -189,16 +190,9 @@ export default function ModerationSettingsPage() {
                                             textDecoration: 'none',
                                         }}
                                     >
-                                        <img
-                                            src={user.avatarUrl || '/default-avatar.png'}
-                                            alt=""
-                                            style={{
-                                                width: '40px',
-                                                height: '40px',
-                                                borderRadius: '50%',
-                                                objectFit: 'cover',
-                                            }}
-                                        />
+                                        <div className="avatar">
+                                            <AvatarImage avatarUrl={user.avatarUrl} seed={user.handle} alt={user.displayName || user.handle} />
+                                        </div>
                                         <div>
                                             <div style={{ fontWeight: 500 }}>
                                                 {user.displayName || user.handle}
diff --git a/src/app/u/[handle]/page.tsx b/src/app/u/[handle]/page.tsx
index 0f693f9..8e8e271 100644
--- a/src/app/u/[handle]/page.tsx
+++ b/src/app/u/[handle]/page.tsx
@@ -13,6 +13,7 @@ import { useFormattedHandle } from '@/lib/utils/handle';
 import { Bot } from 'lucide-react';
 import { useAuth } from '@/lib/contexts/AuthContext';
 import { signedAPI } from '@/lib/api/signed-fetch';
+import { AvatarImage } from '@/components/AvatarImage';
 
 interface BotOwner {
     id: string;
@@ -41,11 +42,7 @@ function UserRow({ user }: { user: UserSummary }) {
     return (
         <Link href={`/u/${user.handle}`} className="user-row">
             <div className="avatar">
-                {user.avatarUrl ? (
-                    <img src={user.avatarUrl} alt={user.displayName || user.handle} />
-                ) : (
-                    (user.displayName || user.handle).charAt(0).toUpperCase()
-                )}
+                <AvatarImage avatarUrl={user.avatarUrl} seed={user.handle} alt={user.displayName || user.handle} />
             </div>
             <div className="user-row-content">
                 <div style={{ display: 'flex', alignItems: 'center', gap: '6px' }}>
@@ -568,11 +565,7 @@ export default function ProfilePage() {
                                 position: 'relative',
                             }}
                         >
-                            {(isEditing ? profileForm.avatarUrl : user.avatarUrl) ? (
-                                <img src={(isEditing ? profileForm.avatarUrl : user.avatarUrl) || ''} alt={user.displayName || user.handle} />
-                            ) : (
-                                (user.displayName || user.handle).charAt(0).toUpperCase()
-                            )}
+                            <AvatarImage avatarUrl={isEditing ? profileForm.avatarUrl : user.avatarUrl} seed={user.handle} alt={user.displayName || user.handle} />
                         </div>
 
                         <div style={{ paddingTop: '12px', display: 'flex', gap: '8px', alignItems: 'center' }}>
diff --git a/src/components/AvatarImage.test.ts b/src/components/AvatarImage.test.ts
new file mode 100644
index 0000000..1c98a4e
--- /dev/null
+++ b/src/components/AvatarImage.test.ts
@@ -0,0 +1,10 @@
+import { describe, expect, it } from 'vitest';
+import { getDiceBearAvatarUrl } from './AvatarImage';
+
+describe('getDiceBearAvatarUrl', () => {
+    it('uses the site-wide bottts-neutral style and a stable encoded handle seed', () => {
+        expect(getDiceBearAvatarUrl('cyph3r@node.example')).toBe(
+            'https://api.dicebear.com/9.x/bottts-neutral/svg?seed=cyph3r%40node.example',
+        );
+    });
+});
diff --git a/src/components/AvatarImage.tsx b/src/components/AvatarImage.tsx
new file mode 100644
index 0000000..accca3d
--- /dev/null
+++ b/src/components/AvatarImage.tsx
@@ -0,0 +1,30 @@
+'use client';
+
+import { useState, type ImgHTMLAttributes } from 'react';
+
+export function getDiceBearAvatarUrl(seed: string): string {
+    return `https://api.dicebear.com/9.x/bottts-neutral/svg?seed=${encodeURIComponent(seed)}`;
+}
+
+interface AvatarImageProps extends Omit<ImgHTMLAttributes<HTMLImageElement>, 'src'> {
+    avatarUrl?: string | null;
+    seed: string;
+}
+
+export function AvatarImage({ avatarUrl, seed, alt = '', onError, ...props }: AvatarImageProps) {
+    const [failedAvatarUrl, setFailedAvatarUrl] = useState<string | null>(null);
+    const customAvatar = avatarUrl?.trim();
+    const src = customAvatar && failedAvatarUrl !== customAvatar ? customAvatar : getDiceBearAvatarUrl(seed);
+
+    return (
+        <img
+            {...props}
+            src={src}
+            alt={alt}
+            onError={(event) => {
+                onError?.(event);
+                if (customAvatar && failedAvatarUrl !== customAvatar) setFailedAvatarUrl(customAvatar);
+            }}
+        />
+    );
+}
diff --git a/src/components/PostCard.tsx b/src/components/PostCard.tsx
index d57ea23..38dc5fc 100644
--- a/src/components/PostCard.tsx
+++ b/src/components/PostCard.tsx
@@ -14,6 +14,7 @@ import { useFormattedHandle } from '@/lib/utils/handle';
 import { useDomain } from '@/lib/contexts/ConfigContext';
 import { signedAPI } from '@/lib/api/signed-fetch';
 import type { LinkPreviewData } from '@/lib/media/linkPreview';
+import { AvatarImage } from '@/components/AvatarImage';
 
 // Component for link preview image that hides on error
 function LinkPreviewImage({ src, alt }: { src: string; alt: string }) {
@@ -638,11 +639,7 @@ export function PostCard({ post, onLike, onRepost, onComment, onDelete, onHide,
                 <div className="post-header">
                     <Link href={`/u/${profileHandle}`} className="avatar-link" onClick={(e) => e.stopPropagation()}>
                         <div className="avatar">
-                            {post.author.avatarUrl ? (
-                                <img src={post.author.avatarUrl} alt={post.author.displayName || ''} />
-                            ) : (
-                                post.author.displayName?.charAt(0).toUpperCase() || post.author.handle.charAt(0).toUpperCase()
-                            )}
+                            <AvatarImage avatarUrl={post.author.avatarUrl} seed={post.author.handle} alt={post.author.displayName || post.author.handle} />
                         </div>
                     </Link>
                     <div className="post-author">
@@ -720,11 +717,7 @@ export function PostCard({ post, onLike, onRepost, onComment, onDelete, onHide,
                 <div className="post-header">
                     <Link href={`/u/${profileHandle}`} className="avatar-link" onClick={(e) => e.stopPropagation()}>
                         <div className="avatar">
-                            {post.author.avatarUrl ? (
-                                <img src={post.author.avatarUrl} alt={post.author.displayName} />
-                            ) : (
-                                post.author.displayName?.charAt(0).toUpperCase() || post.author.handle.charAt(0).toUpperCase()
-                            )}
+                            <AvatarImage avatarUrl={post.author.avatarUrl} seed={post.author.handle} alt={post.author.displayName || post.author.handle} />
                         </div>
                     </Link>
                     <div className="post-author">
diff --git a/src/components/RightSidebar.tsx b/src/components/RightSidebar.tsx
index ebc29fe..7b441a6 100644
--- a/src/components/RightSidebar.tsx
+++ b/src/components/RightSidebar.tsx
@@ -2,6 +2,7 @@
 
 import { useState, useEffect } from 'react';
 import Link from 'next/link';
+import { AvatarImage } from './AvatarImage';
 
 interface Admin {
     handle: string;
@@ -136,11 +137,7 @@ export function RightSidebar() {
                                     style={{ display: 'flex', alignItems: 'center', gap: '10px', textDecoration: 'none', color: 'inherit' }}
                                 >
                                     <div className="avatar avatar-sm" style={{ flexShrink: 0 }}>
-                                        {admin.avatarUrl ? (
-                                            <img src={admin.avatarUrl} alt={admin.displayName || admin.handle} />
-                                        ) : (
-                                            (admin.displayName?.charAt(0) || admin.handle.charAt(0)).toUpperCase()
-                                        )}
+                                        <AvatarImage avatarUrl={admin.avatarUrl} seed={admin.handle} alt={admin.displayName || admin.handle} />
                                     </div>
                                     <div>
                                         <div style={{ fontWeight: 500, fontSize: '14px' }}>
diff --git a/src/components/Sidebar.tsx b/src/components/Sidebar.tsx
index a4faae1..0348b79 100644
--- a/src/components/Sidebar.tsx
+++ b/src/components/Sidebar.tsx
@@ -10,6 +10,7 @@ import { HomeIcon, SearchIcon, BellIcon, UserIcon, ShieldIcon, SettingsIcon, Bot
 import { useFormattedHandle } from '@/lib/utils/handle';
 import { Check, ChevronDown, LogOut, Plus, Settings2 } from 'lucide-react';
 import { AuthScreen } from '@/app/login/page';
+import { AvatarImage } from './AvatarImage';
 // import { IdentityUnlockPrompt } from './IdentityUnlockPrompt'; // Moved to LayoutWrapper
 
 function shortHandle(handle: string) {
@@ -327,11 +328,7 @@ export function Sidebar() {
                                             }}
                                         >
                                             <div className="avatar avatar-sm" style={{ flexShrink: 0 }}>
-                                                {account.avatarUrl ? (
-                                                    <img src={account.avatarUrl} alt={account.displayName || account.handle} style={{ width: '100%', height: '100%', objectFit: 'cover' }} />
-                                                ) : (
-                                                    (account.displayName?.charAt(0) || account.handle.charAt(0)).toUpperCase()
-                                                )}
+                                                <AvatarImage avatarUrl={account.avatarUrl} seed={account.handle} alt={account.displayName || account.handle} />
                                             </div>
                                             <div style={{ minWidth: 0, flex: 1, display: 'grid', gap: '2px' }}>
                                                 <div style={{ fontWeight: 700, fontSize: '15px', lineHeight: 1.2, overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>
@@ -418,11 +415,7 @@ export function Sidebar() {
                         }}
                     >
                         <div className="avatar avatar-sm" style={{ flexShrink: 0 }}>
-                            {user.avatarUrl ? (
-                                <img src={user.avatarUrl} alt={user.displayName} style={{ width: '100%', height: '100%', objectFit: 'cover' }} />
-                            ) : (
-                                (user.displayName?.charAt(0) || user.handle.charAt(0)).toUpperCase()
-                            )}
+                            <AvatarImage avatarUrl={user.avatarUrl} seed={user.handle} alt={user.displayName} />
                         </div>
                         <div style={{ minWidth: 0, flex: 1, textAlign: 'left' }}>
                             <div style={{ fontWeight: 600, fontSize: '14px', overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>{user.displayName}</div>