diff --git a/public/admin.html b/public/admin.html
index 1aae1d5..da786ea 100644
--- a/public/admin.html
+++ b/public/admin.html
@@ -34,6 +34,7 @@
   }
   button:disabled { opacity: .5; cursor: default; }
   button.danger { background: transparent; color: #d33; padding: 4px 8px; font-weight: 400; }
+  button.plain { background: transparent; color: #2b6cf5; padding: 4px 8px; font-weight: 400; }
   button.big { padding: 12px 28px; }
   table { width: 100%; border-collapse: collapse; font-size: 14px; }
   th { text-align: left; font-size: 12px; color: #6b7590; font-weight: 500; padding: 6px 8px; }
@@ -50,6 +51,30 @@
   #msg.err { color: #d33; }
   .muted { color: #6b7590; font-size: 13px; }
   progress { width: 240px; }
+  #cropModal {
+    position: fixed; inset: 0; z-index: 100; display: flex;
+    align-items: center; justify-content: center; padding: 20px;
+    background: rgba(0, 0, 0, .55);
+  }
+  #cropModal[hidden] { display: none; }
+  #cropPanel {
+    background: #fff; border-radius: 12px; padding: 20px;
+    max-width: 560px; max-height: 92vh; overflow: auto;
+  }
+  @media (prefers-color-scheme: dark) { #cropPanel { background: #1a1f2b; } }
+  #cropPanel h2 { font-size: 16px; margin: 0 0 8px; }
+  #cropStage {
+    position: relative; display: inline-block; margin-top: 10px;
+    touch-action: none; user-select: none; overflow: hidden; border-radius: 8px;
+  }
+  #cropImg { display: block; max-width: 100%; max-height: 58vh; }
+  #cropRect {
+    position: absolute; border: 2px solid #2b6cf5; pointer-events: none;
+    box-shadow: 0 0 0 9999px rgba(0, 0, 0, .5);
+  }
+  #cropMsg { min-height: 1.4em; margin-top: 8px; }
+  #cropMsg.err { color: #d33; }
+  .cropBtns { display: flex; gap: 10px; justify-content: flex-end; margin-top: 12px; }
 </style>
 </head>
 <body>
@@ -82,6 +107,24 @@
     </table>
   </div>
 
+  <div id="cropModal" hidden>
+    <div id="cropPanel">
+      <h2>框選辨識主體</h2>
+      <p class="muted" style="margin:0">
+        在照片上拖曳，框出最有辨識度的區域（例如人物）。背景相似的多張照片各自框選主體後，
+        掃描就不會互相認錯；影片播放時仍會覆蓋整張照片。
+        框的長寬至少要佔照片 15%，框太小特徵點不足反而難辨識。改完記得重新編譯。
+      </p>
+      <div id="cropStage"><img id="cropImg" draggable="false"><div id="cropRect" hidden></div></div>
+      <div id="cropMsg" class="muted"></div>
+      <div class="cropBtns">
+        <button type="button" id="cropClear" class="danger">清除（用整張照片）</button>
+        <button type="button" id="cropCancel" style="background:#6b7590">取消</button>
+        <button type="button" id="cropSave">儲存</button>
+      </div>
+    </div>
+  </div>
+
 <script>
 let state = null;
 
@@ -131,6 +174,12 @@ async function refresh() {
     tdTime.textContent = new Date(p.createdAt).toLocaleString();
 
     const tdDel = document.createElement('td');
+    const cropBtn = document.createElement('button');
+    cropBtn.className = 'plain';
+    cropBtn.textContent = p.crop ? '主體✓' : '框主體';
+    cropBtn.title = '框選辨識主體（背景相似的照片才不會互相認錯）';
+    cropBtn.onclick = () => openCropModal(p);
+    tdDel.appendChild(cropBtn);
     const del = document.createElement('button');
     del.className = 'danger';
     del.textContent = '刪除';
@@ -150,6 +199,99 @@ async function refresh() {
 // 且掃描端（尤其 iOS Safari）的 WebGL 記憶體撐得住
 const MAX_EDGE = 1280;
 
+// ---- 框選辨識主體（裁切框只影響編譯輸入，照片檔不動）----
+const cropModal = document.getElementById('cropModal');
+const cropStage = document.getElementById('cropStage');
+const cropImg = document.getElementById('cropImg');
+const cropRect = document.getElementById('cropRect');
+const cropMsg = document.getElementById('cropMsg');
+const CROP_MIN = 0.15; // 框的長寬至少要佔照片的比例
+
+let cropPair = null;
+let cropRel = null; // {x,y,w,h} 相對座標，null = 整張照片
+
+function openCropModal(pair) {
+  cropPair = pair;
+  cropRel = pair.crop ? { ...pair.crop } : null;
+  cropMsg.className = 'muted';
+  cropMsg.textContent = '';
+  cropImg.src = '/data/photos/' + encodeURIComponent(pair.photo) + '?t=' + pair.createdAt;
+  cropModal.hidden = false;
+  if (cropImg.complete) renderCropRect();
+  else cropImg.onload = renderCropRect;
+}
+
+function renderCropRect() {
+  if (!cropRel) {
+    cropRect.hidden = true;
+    return;
+  }
+  cropRect.hidden = false;
+  cropRect.style.left = cropRel.x * cropImg.clientWidth + 'px';
+  cropRect.style.top = cropRel.y * cropImg.clientHeight + 'px';
+  cropRect.style.width = cropRel.w * cropImg.clientWidth + 'px';
+  cropRect.style.height = cropRel.h * cropImg.clientHeight + 'px';
+}
+
+// 拖曳畫框（pointer events 同時支援滑鼠與觸控）
+let dragStart = null;
+function pointToRel(e) {
+  const r = cropImg.getBoundingClientRect();
+  return {
+    x: Math.min(1, Math.max(0, (e.clientX - r.left) / r.width)),
+    y: Math.min(1, Math.max(0, (e.clientY - r.top) / r.height)),
+  };
+}
+cropStage.addEventListener('pointerdown', (e) => {
+  e.preventDefault();
+  cropStage.setPointerCapture(e.pointerId);
+  dragStart = pointToRel(e);
+});
+cropStage.addEventListener('pointermove', (e) => {
+  if (!dragStart) return;
+  const p = pointToRel(e);
+  cropRel = {
+    x: Math.min(dragStart.x, p.x),
+    y: Math.min(dragStart.y, p.y),
+    w: Math.abs(p.x - dragStart.x),
+    h: Math.abs(p.y - dragStart.y),
+  };
+  renderCropRect();
+});
+cropStage.addEventListener('pointerup', () => { dragStart = null; });
+window.addEventListener('resize', () => {
+  if (!cropModal.hidden) renderCropRect();
+});
+
+document.getElementById('cropClear').onclick = () => {
+  cropRel = null;
+  renderCropRect();
+  cropMsg.className = 'muted';
+  cropMsg.textContent = '已清除，按「儲存」後會改用整張照片。';
+};
+document.getElementById('cropCancel').onclick = () => { cropModal.hidden = true; };
+document.getElementById('cropSave').onclick = async () => {
+  if (cropRel && (cropRel.w < CROP_MIN || cropRel.h < CROP_MIN)) {
+    cropMsg.className = 'err';
+    cropMsg.textContent = `框太小了：長寬都要至少佔照片 ${CROP_MIN * 100}%，不然特徵點不足難以辨識。`;
+    return;
+  }
+  try {
+    const res = await fetch('/api/pairs/' + cropPair.id + '/crop', {
+      method: 'PUT',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ crop: cropRel }),
+    });
+    const json = await res.json();
+    if (!res.ok) throw new Error(json.error || res.statusText);
+    cropModal.hidden = true;
+    refresh();
+  } catch (err) {
+    cropMsg.className = 'err';
+    cropMsg.textContent = '儲存失敗：' + err.message;
+  }
+};
+
 function loadImageFromFile(file) {
   return new Promise((resolve, reject) => {
     const url = URL.createObjectURL(file);
@@ -251,17 +393,23 @@ document.getElementById('compileBtn').addEventListener('click', async () => {
       pairs.map((p) => loadImage('/data/photos/' + encodeURIComponent(p.photo)))
     );
 
+    // 有框選主體的配對只用框內區域編譯（背景相似的照片才不會互相認錯）。
     // 大圖先縮到長邊 MAX_EDGE 再編譯（雙保險：新上傳的照片已在上傳時縮圖，
     // 這裡再保護縮圖修正前上傳的舊照片）。
     // 曾發生 4 張 2244x4131 原圖直接編譯後，iPhone 掃任何照片都沒反應
     // （桌面 Chrome 正常，iOS WebGL 資源上限較低，辨識引擎無聲掛掉）
-    const compileInputs = images.map((img) => {
-      const scale = Math.min(1, MAX_EDGE / Math.max(img.naturalWidth, img.naturalHeight));
-      if (scale === 1) return img;
+    const compileInputs = images.map((img, i) => {
+      const crop = pairs[i].crop;
+      const sx = crop ? crop.x * img.naturalWidth : 0;
+      const sy = crop ? crop.y * img.naturalHeight : 0;
+      const sw = crop ? crop.w * img.naturalWidth : img.naturalWidth;
+      const sh = crop ? crop.h * img.naturalHeight : img.naturalHeight;
+      const scale = Math.min(1, MAX_EDGE / Math.max(sw, sh));
+      if (scale === 1 && !crop) return img;
       const c = document.createElement('canvas');
-      c.width = Math.round(img.naturalWidth * scale);
-      c.height = Math.round(img.naturalHeight * scale);
-      c.getContext('2d').drawImage(img, 0, 0, c.width, c.height);
+      c.width = Math.round(sw * scale);
+      c.height = Math.round(sh * scale);
+      c.getContext('2d').drawImage(img, sx, sy, sw, sh, 0, 0, c.width, c.height);
       return c;
     });
 
@@ -274,10 +422,13 @@ document.getElementById('compileBtn').addEventListener('click', async () => {
     const buffer = await compiler.exportData();
 
     status.textContent = '上傳特徵檔…';
+    // aspect 一律是整張照片的長寬比；有裁切時另外附上裁切框，
+    // 掃描頁靠這兩個值把影片平面校正回「覆蓋整張照片」
     const mapping = {
       targets: pairs.map((p, i) => ({
         pairId: p.id,
         aspect: images[i].naturalHeight / images[i].naturalWidth,
+        crop: p.crop || undefined,
       })),
     };
     const fd = new FormData();
diff --git a/public/index.html b/public/index.html
index 7aa1fb7..1a81b47 100644
--- a/public/index.html
+++ b/public/index.html
@@ -78,7 +78,7 @@
     <p id="status">載入中…</p>
     <button id="startBtn" hidden>開始掃描</button>
     <p class="hint">按下開始後，將相機對準已登錄的照片，<br>對應的影片就會覆蓋在照片上播放。</p>
-    <p class="hint" style="font-size:11px">v8</p>
+    <p class="hint" style="font-size:11px">v9</p>
   </div>
   <button id="stopBtn" title="停止">✕</button>
   <a id="dlBtn" title="下載影片" download>⬇</a>
@@ -209,12 +209,24 @@ function buildScene(version, entries) {
     const anchor = document.createElement('a-entity');
     anchor.setAttribute('mindar-image-target', 'targetIndex: ' + t.index);
 
-    // MindAR 的目標寬度固定為 1，用照片長寬比讓影片剛好蓋住整張照片
+    // MindAR 的目標寬度固定為 1（辨識目標＝編譯輸入的那塊影像）。
+    // 沒裁切時目標就是整張照片，影片平面直接用照片長寬比；
+    // 有框選主體時目標只是照片的一塊，要按裁切框把影片平面放大並平移，
+    // 讓影片仍然剛好覆蓋整張照片（座標換算：1 目標單位 = 裁切框寬）
+    const aspect = t.aspect || 1;
+    const crop = t.crop;
+    let pw = 1, ph = aspect, px = 0, py = 0;
+    if (crop && crop.w > 0 && crop.h > 0) {
+      pw = 1 / crop.w;
+      ph = aspect / crop.w;
+      px = (0.5 - crop.x - crop.w / 2) / crop.w;
+      py = -(0.5 - crop.y - crop.h / 2) * aspect / crop.w;
+    }
     const plane = document.createElement('a-video');
     plane.setAttribute('src', '#vid-' + t.index);
-    plane.setAttribute('width', '1');
-    plane.setAttribute('height', String(t.aspect || 1));
-    plane.setAttribute('position', '0 0 0');
+    plane.setAttribute('width', String(pw));
+    plane.setAttribute('height', String(ph));
+    plane.setAttribute('position', `${px} ${py} 0`);
     anchor.appendChild(plane);
 
     let isFound = false;
diff --git a/server.js b/server.js
index a681525..fe2b517 100644
--- a/server.js
+++ b/server.js
@@ -137,6 +137,28 @@ shared.post(
   }
 );
 
+// 裁切框（相對座標 0~1，null 表示用整張照片）。只影響編譯輸入，照片檔不動
+function isValidCrop(c) {
+  if (c === null) return true;
+  if (!c || typeof c !== 'object') return false;
+  const nums = [c.x, c.y, c.w, c.h];
+  if (!nums.every((n) => typeof n === 'number' && Number.isFinite(n))) return false;
+  return c.x >= 0 && c.y >= 0 && c.w > 0 && c.h > 0 && c.x + c.w <= 1.0001 && c.y + c.h <= 1.0001;
+}
+
+shared.put('/api/pairs/:id/crop', express.json(), (req, res) => {
+  const pair = db.pairs.find((p) => p.id === req.params.id);
+  if (!pair) return res.status(404).json({ error: '找不到這組配對' });
+  const crop = req.body ? req.body.crop : undefined;
+  if (crop === undefined || !isValidCrop(crop)) {
+    return res.status(400).json({ error: 'crop 格式錯誤（需為 null 或 {x,y,w,h} 相對座標）' });
+  }
+  if (crop === null) delete pair.crop;
+  else pair.crop = { x: +crop.x.toFixed(4), y: +crop.y.toFixed(4), w: +crop.w.toFixed(4), h: +crop.h.toFixed(4) };
+  persistDb();
+  res.json({ ok: true, pair });
+});
+
 shared.delete('/api/pairs/:id', (req, res) => {
   const idx = db.pairs.findIndex((p) => p.id === req.params.id);
   if (idx === -1) return res.status(404).json({ error: '找不到這組配對' });
