diff --git a/docs/MONETIZATION.md b/docs/MONETIZATION.md
index 75e893c..5e32a3b 100644
--- a/docs/MONETIZATION.md
+++ b/docs/MONETIZATION.md
@@ -41,8 +41,9 @@
 - Proof-of-Work basiert, kein Tracking
 - Keine externe Abhängigkeit, keine Lizenzkosten
 - Client löst SHA256-Challenge (Difficulty 4, ~1-3 Sek)
-- Bei Account-Erstellung
-- Bei Anzeigen-Erstellung
+- Bei Account-Erstellung (immer)
+- Bei Anzeigen-Erstellung (immer)
+- Bei Login (nur nach 3+ Fehlversuchen)
 - Implementierung: `js/services/pow-captcha.js`, `js/components/pow-captcha.js`
 
 ## Payment-Integration
diff --git a/js/components/auth-modal.js b/js/components/auth-modal.js
index 297b765..70ae744 100644
--- a/js/components/auth-modal.js
+++ b/js/components/auth-modal.js
@@ -4,6 +4,7 @@
 
 import { t, i18n } from '../i18n.js'
 import { auth } from '../services/auth.js'
+import './pow-captcha.js'
 
 class AuthModal extends HTMLElement {
     constructor() {
@@ -12,6 +13,7 @@ class AuthModal extends HTMLElement {
         this.generatedUuid = null
         this.error = null
         this.loading = false
+        this.loginAttempts = 0
     }
 
     connectedCallback() {
@@ -94,6 +96,12 @@ class AuthModal extends HTMLElement {
                     >
                 </div>
 
+                ${this.loginAttempts >= 3 ? `
+                    <div class="form-group">
+                        <pow-captcha id="login-captcha"></pow-captcha>
+                    </div>
+                ` : ''}
+
                 <button type="submit" class="btn btn-primary btn-lg btn-block" ${this.loading ? 'disabled' : ''}>
                     ${this.loading ? t('auth.loggingIn') : t('auth.login')}
                 </button>
@@ -117,6 +125,10 @@ class AuthModal extends HTMLElement {
 
             ${this.error ? `<div class="auth-error">${this.error}</div>` : ''}
 
+            <div class="form-group">
+                <pow-captcha id="register-captcha"></pow-captcha>
+            </div>
+
             <button 
                 class="btn btn-primary btn-lg btn-block" 
                 id="generate-uuid"
@@ -210,6 +222,16 @@ class AuthModal extends HTMLElement {
             return
         }
 
+        // Check captcha after 3 failed attempts
+        if (this.loginAttempts >= 3) {
+            const captcha = this.querySelector('#login-captcha')
+            if (!captcha?.isSolved()) {
+                this.error = t('captcha.error')
+                this.render()
+                return
+            }
+        }
+
         this.loading = true
         this.error = null
         this.render()
@@ -219,18 +241,34 @@ class AuthModal extends HTMLElement {
         this.loading = false
 
         if (result.success) {
+            this.loginAttempts = 0
             this.hide()
             this.dispatchEvent(new CustomEvent('login', { detail: { success: true } }))
         } else {
+            this.loginAttempts++
             this.error = result.error || t('auth.invalidUuid')
             this.render()
         }
     }
 
     async handleRegister() {
+        // Require captcha for registration
+        const captcha = this.querySelector('#register-captcha')
+        if (!captcha?.isSolved()) {
+            this.error = t('captcha.error')
+            this.render()
+            return
+        }
+
         this.loading = true
         this.error = null
-        this.render()
+        
+        // Update button state without full re-render (keeps captcha state)
+        const btn = this.querySelector('#generate-uuid')
+        if (btn) {
+            btn.disabled = true
+            btn.textContent = t('auth.creating')
+        }
 
         const result = await auth.createAccount()
 
diff --git a/js/components/pow-captcha.js b/js/components/pow-captcha.js
index f778660..1af3e06 100644
--- a/js/components/pow-captcha.js
+++ b/js/components/pow-captcha.js
@@ -6,6 +6,7 @@ export class PowCaptcha extends HTMLElement {
   constructor() {
     super()
     this.solved = false
+    this.solving = false
     this.solution = null
     this.unsubscribe = null
   }
@@ -21,46 +22,42 @@ export class PowCaptcha extends HTMLElement {
 
   render() {
     this.innerHTML = `
-      <div class="pow-captcha">
-        <div class="pow-captcha-status">
-          ${this.solved 
-            ? `<span class="pow-captcha-success">✓ ${t('captcha.verified')}</span>`
-            : `<button class="pow-captcha-btn" type="button">${t('captcha.verify')}</button>`
-          }
-        </div>
-        <div class="pow-captcha-progress" style="display: none;">
-          <div class="pow-captcha-progress-bar"></div>
-          <span class="pow-captcha-progress-text"></span>
-        </div>
+      <div class="pow-captcha ${this.solved ? 'pow-captcha--solved' : ''} ${this.solving ? 'pow-captcha--solving' : ''}">
+        <label class="pow-captcha-label">
+          <span class="pow-captcha-checkbox">
+            ${this.solved 
+              ? `<svg class="pow-captcha-check" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="3">
+                   <polyline points="20 6 9 17 4 12"></polyline>
+                 </svg>`
+              : this.solving
+                ? `<span class="pow-captcha-spinner"></span>`
+                : ``
+            }
+          </span>
+          <span class="pow-captcha-text">
+            ${this.solved ? t('captcha.verified') : t('captcha.verify')}
+          </span>
+        </label>
       </div>
     `
 
-    if (!this.solved) {
-      this.querySelector('.pow-captcha-btn').addEventListener('click', () => this.solve())
+    if (!this.solved && !this.solving) {
+      this.querySelector('.pow-captcha-label').addEventListener('click', () => this.solve())
     }
   }
 
   async solve() {
-    const btn = this.querySelector('.pow-captcha-btn')
-    const progress = this.querySelector('.pow-captcha-progress')
-    const progressBar = this.querySelector('.pow-captcha-progress-bar')
-    const progressText = this.querySelector('.pow-captcha-progress-text')
+    if (this.solving || this.solved) return
 
-    btn.disabled = true
-    btn.textContent = t('captcha.solving')
-    progress.style.display = 'flex'
+    this.solving = true
+    this.render()
 
     try {
       // Generate challenge (in production, fetch from server)
       const { challenge, difficulty, timestamp, signature } = generateChallenge()
 
-      // Solve with progress updates
-      const result = await solveChallenge(challenge, difficulty, ({ attempts, elapsed }) => {
-        const estimatedTotal = Math.pow(16, difficulty) / 2
-        const percent = Math.min((attempts / estimatedTotal) * 100, 95)
-        progressBar.style.width = `${percent}%`
-        progressText.textContent = `${attempts.toLocaleString()} ${t('captcha.attempts')}`
-      })
+      // Solve challenge
+      const result = await solveChallenge(challenge, difficulty)
 
       // Store solution for form submission
       this.solution = {
@@ -70,13 +67,14 @@ export class PowCaptcha extends HTMLElement {
         timestamp
       }
 
+      this.solving = false
       this.solved = true
       this.dispatchEvent(new CustomEvent('solved', { detail: this.solution }))
       this.render()
 
     } catch (error) {
-      btn.disabled = false
-      btn.textContent = t('captcha.error')
+      this.solving = false
+      this.render()
       console.error('PoW Captcha error:', error)
     }
   }
@@ -105,52 +103,74 @@ customElements.define('pow-captcha', PowCaptcha)
 const style = document.createElement('style')
 style.textContent = `
   .pow-captcha {
-    padding: var(--space-md);
+    display: inline-block;
+    padding: var(--space-md) var(--space-lg);
     border: 1px solid var(--color-border);
     border-radius: var(--radius-md);
-    background: var(--color-surface);
+    background: var(--color-surface, var(--color-bg-secondary));
   }
 
-  .pow-captcha-btn {
-    padding: var(--space-sm) var(--space-md);
-    background: var(--color-primary);
-    color: var(--color-bg);
-    border: none;
-    border-radius: var(--radius-sm);
+  .pow-captcha-label {
+    display: flex;
+    align-items: center;
+    gap: var(--space-md);
     cursor: pointer;
+    user-select: none;
+  }
+
+  .pow-captcha--solving .pow-captcha-label,
+  .pow-captcha--solved .pow-captcha-label {
+    cursor: default;
+  }
+
+  .pow-captcha-checkbox {
+    width: 24px;
+    height: 24px;
+    border: 2px solid var(--color-border);
+    border-radius: var(--radius-sm);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    background: var(--color-bg);
+    transition: all 0.2s ease;
+  }
+
+  .pow-captcha:hover:not(.pow-captcha--solved):not(.pow-captcha--solving) .pow-captcha-checkbox {
+    border-color: var(--color-primary);
+  }
+
+  .pow-captcha--solved .pow-captcha-checkbox {
+    background: var(--color-success, #22c55e);
+    border-color: var(--color-success, #22c55e);
+  }
+
+  .pow-captcha-check {
+    width: 16px;
+    height: 16px;
+    color: white;
+  }
+
+  .pow-captcha-spinner {
+    width: 16px;
+    height: 16px;
+    border: 2px solid var(--color-border);
+    border-top-color: var(--color-primary);
+    border-radius: 50%;
+    animation: pow-spin 0.8s linear infinite;
+  }
+
+  @keyframes pow-spin {
+    to { transform: rotate(360deg); }
+  }
+
+  .pow-captcha-text {
     font-size: var(--font-size-sm);
+    color: var(--color-text);
   }
 
-  .pow-captcha-btn:disabled {
-    opacity: 0.6;
-    cursor: wait;
-  }
-
-  .pow-captcha-success {
+  .pow-captcha--solved .pow-captcha-text {
     color: var(--color-success, #22c55e);
     font-weight: 500;
   }
-
-  .pow-captcha-progress {
-    margin-top: var(--space-sm);
-    align-items: center;
-    gap: var(--space-sm);
-  }
-
-  .pow-captcha-progress-bar {
-    height: 4px;
-    background: var(--color-primary);
-    border-radius: 2px;
-    width: 0%;
-    transition: width 0.1s;
-    flex: 1;
-  }
-
-  .pow-captcha-progress-text {
-    font-size: var(--font-size-xs);
-    color: var(--color-text-muted);
-    min-width: 100px;
-    text-align: right;
-  }
 `
 document.head.appendChild(style)