diff --git a/README.md b/README.md
index 1982e71..fe92785 100644
--- a/README.md
+++ b/README.md
@@ -32,6 +32,23 @@ docker compose exec rustdesk cat /data/id_ed25519.pub
 
 **RustDesk client:** ID Server `your-server:21116`, Relay `your-server:21117`, API `http://your-server:21114`, Key — paste the public-key contents returned by `docker compose exec rustdesk cat /data/id_ed25519.pub`; the file is at `/data/id_ed25519.pub` inside the container.
 
+## Upgrading an existing deployment
+
+The Compose file bind-mounts `../data/uploads` to `/app/resources/public/upload`.
+On an existing deployment the mount shadows the uploads already stored inside the
+old container, so branding assets referenced before the mount (`GET /upload/...`)
+return 404. Copy them out of the old container before the first `docker compose
+up -d` with the new mount:
+
+```bash
+mkdir -p ../data/uploads
+docker cp <old-rustdesk-container>:/app/resources/public/upload/. ../data/uploads/
+docker compose up -d
+```
+
+This migration applies only to the upload bind mount; other data (`/data`, the
+database) stays on its existing volumes.
+
 ---
 
 ## Ports
diff --git a/admin-ui/src/components/ui/ImageAttachField.vue b/admin-ui/src/components/ui/ImageAttachField.vue
index 32a0ccd..5374a42 100644
--- a/admin-ui/src/components/ui/ImageAttachField.vue
+++ b/admin-ui/src/components/ui/ImageAttachField.vue
@@ -1,6 +1,6 @@
 <template>
   <div class="image-attach-field">
-    <div class="image-attach-field__preview" :aria-label="modelValue && !previewFailed ? undefined : previewEmptyLabel">
+    <div class="image-attach-field__preview" :aria-label="previewAriaLabel">
       <img
         v-if="modelValue && !previewFailed"
         :src="modelValue"
@@ -8,6 +8,19 @@
         class="image-attach-field__image"
         @error="previewFailed = true"
       >
+      <span
+        v-else-if="previewFailed"
+        class="image-attach-field__unavailable"
+        tabindex="0"
+        :aria-label="unavailableLabel"
+      >
+        <el-tooltip :content="unavailableDetails" placement="top" popper-class="image-attach-field-hint-popper">
+          <span class="image-attach-field__unavailable-chip">
+            <el-icon aria-hidden="true"><WarningFilled /></el-icon>
+            <span aria-hidden="true">{{ unavailableLabel }}</span>
+          </span>
+        </el-tooltip>
+      </span>
       <span v-else class="image-attach-field__placeholder">
         <el-icon aria-hidden="true"><Picture /></el-icon>
       </span>
@@ -50,8 +63,8 @@
 </template>
 
 <script setup>
-import { ref, watch } from 'vue'
-import { Close, InfoFilled, Picture } from '@element-plus/icons-vue'
+import { computed, ref, watch } from 'vue'
+import { Close, InfoFilled, Picture, WarningFilled } from '@element-plus/icons-vue'
 
 const props = defineProps({
   modelValue: { type: String, default: '' },
@@ -64,6 +77,11 @@ const props = defineProps({
   linkPlaceholder: { type: String, default: '' },
   clearLabel: { type: String, default: '' },
   previewEmptyLabel: { type: String, default: '' },
+  // Explicit unavailable state for a preview URL that failed to load (404 or
+  // otherwise unreachable): a warning message, never a validation error —
+  // the field is optional and the file may only be temporarily unreachable.
+  unavailableLabel: { type: String, default: '' },
+  unavailableDetails: { type: String, default: '' },
   // Allowed-range hover text (variants/limits). Required format lives in the
   // permanent note below the input; mechanics live in the section note.
   rangeHint: { type: String, default: '' },
@@ -74,11 +92,20 @@ const props = defineProps({
 
 const emit = defineEmits(['update:modelValue', 'input'])
 
-// A broken preview URL degrades to the neutral placeholder; a new value
-// (typed or uploaded) retries the preview automatically.
+// Preview failed-state flag, declared before the computed below that reads it:
+// it is a local ref, not a prop (props.previewFailed was always undefined),
+// and the computed must read `previewFailed.value`. A new value (typed or
+// uploaded) resets the flag, retrying the preview automatically.
 const previewFailed = ref(false)
 watch(() => props.modelValue, () => { previewFailed.value = false })
 
+// Preview state labels: visible image needs no label; a failed load names the
+// unavailable state; an empty preview keeps the neutral no-preview label.
+const previewAriaLabel = computed(() => {
+  if (!props.modelValue) return props.previewEmptyLabel
+  return previewFailed.value ? props.unavailableLabel : undefined
+})
+
 const clear = () => {
   if (!props.modelValue) return
   previewFailed.value = false
@@ -138,6 +165,41 @@ const onInputEvent = (value) => {
   font-size: 24px;
 }
 
+// Explicit warning state for a preview URL that failed to load — visually a
+// warning, semantically still a plain state message (not a validation error).
+.image-attach-field__unavailable {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 64px;
+  height: 64px;
+  padding: 4px;
+  border: 1px solid var(--el-color-warning-light-5);
+  border-radius: 4px;
+  background: var(--el-color-warning-light-9);
+  color: var(--el-color-warning);
+  text-align: center;
+  cursor: help;
+
+  &:focus-visible {
+    outline: 2px solid var(--el-color-primary);
+    outline-offset: 2px;
+  }
+}
+
+.image-attach-field__unavailable-chip {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 2px;
+  font-size: 10px;
+  line-height: 1.2;
+
+  .el-icon {
+    font-size: 16px;
+  }
+}
+
 .image-attach-field__clear {
   display: inline-flex;
   align-items: center;
diff --git a/admin-ui/src/utils/i18n/en.json b/admin-ui/src/utils/i18n/en.json
index f4f1093..570c308 100644
--- a/admin-ui/src/utils/i18n/en.json
+++ b/admin-ui/src/utils/i18n/en.json
@@ -1139,10 +1139,10 @@
     "One": "App Icon (PNG)"
   },
   "ImageAttachFileButton": {
-    "One": "Upload file (≤5 MB)"
+    "One": "Upload file"
   },
   "ImageAttachLinkPlaceholder": {
-    "One": "or paste http(s)…"
+    "One": "or paste an http(s) link…"
   },
   "ImageAttachClear": {
     "One": "Clear"
@@ -1150,8 +1150,20 @@
   "ImageAttachPreviewEmpty": {
     "One": "No preview"
   },
+  "ImageUnavailable": {
+    "One": "File unavailable"
+  },
+  "ImageUnavailableDetails": {
+    "One": "Could not load — the file may be missing on the server; building with this link will fail at the branding step."
+  },
   "BrandingImagesMechanicsNote": {
-    "One": "Files are stored on the server; at build time the link is automatically resolved against the API server address. A pasted link must be a publicly reachable http(s) URL."
+    "One": "Uploaded files are stored on the server and resolved at build time; paste a publicly reachable http(s) link."
+  },
+  "BrandingPublicOriginMissingTitle": {
+    "One": "Images won't attach to the build"
+  },
+  "BrandingPublicOriginMissing": {
+    "One": "The public API server address is not set. Uploaded images will not be usable in builds: /upload/… values cannot be resolved to a public link. Set the RUSTDESK_API_RUSTDESK_PUBLIC_API_SERVER environment variable in the API environment."
   },
   "AppLogo": {
     "One": "App Logo (PNG)"
@@ -1160,22 +1172,22 @@
     "One": "Privacy screen (PNG)"
   },
   "ImageFieldNoteIcon": {
-    "One": "Required: PNG, square; 256×256 ideal (minimum 16×16)"
+    "One": "PNG · square · 256×256 ideal · file ≤5 MB · link ≤10 MB"
   },
   "ImageFieldNoteLogo": {
-    "One": "Required: PNG; up to 300×60 ideal (render stops at 300×60)"
+    "One": "PNG · up to 300×60 · file ≤5 MB · link ≤10 MB"
   },
   "ImageFieldNoteScreen": {
-    "One": "Required: PNG (shown fullscreen)"
+    "One": "PNG · fullscreen · file ≤5 MB · link ≤20 MB"
   },
   "ImageRangeIcon": {
-    "One": "Accepted: square 16×16–4096×4096; larger than 256×256 is downscaled to 256 for Windows icons; file ≤5 MB, URL ≤10 MB"
+    "One": "Accepted: square 16×16–4096×4096; squares above 256 are downscaled to 256 for Windows icons"
   },
   "ImageRangeLogo": {
-    "One": "Accepted: PNG up to 4096×4096; file ≤5 MB, URL ≤10 MB"
+    "One": "Accepted source: PNG up to 4096×4096"
   },
   "ImageRangeScreen": {
-    "One": "Accepted: PNG up to 4096×4096; file ≤5 MB, URL ≤20 MB"
+    "One": "Accepted source: PNG up to 4096×4096"
   },
   "ImageFieldPngOnlyError": {
     "One": "Only PNG images are allowed"
diff --git a/admin-ui/src/utils/i18n/ru.json b/admin-ui/src/utils/i18n/ru.json
index aeb387d..8342943 100644
--- a/admin-ui/src/utils/i18n/ru.json
+++ b/admin-ui/src/utils/i18n/ru.json
@@ -830,10 +830,10 @@
     "One": "Иконка приложения (PNG)"
   },
   "ImageAttachFileButton": {
-    "One": "Загрузить файл (≤5 МБ)"
+    "One": "Загрузить файл"
   },
   "ImageAttachLinkPlaceholder": {
-    "One": "или вставьте http(s)…"
+    "One": "или вставьте ссылку http(s)…"
   },
   "ImageAttachClear": {
     "One": "Очистить"
@@ -841,8 +841,20 @@
   "ImageAttachPreviewEmpty": {
     "One": "Нет предпросмотра"
   },
+  "ImageUnavailable": {
+    "One": "Файл недоступен"
+  },
+  "ImageUnavailableDetails": {
+    "One": "Не удалось загрузить — файл может отсутствовать на сервере; сборка с такой ссылкой упадёт на брендинге."
+  },
   "BrandingImagesMechanicsNote": {
-    "One": "Файл сохраняется на сервере; при сборке ссылка автоматически подставляется из адреса API-сервера. Вставленная ссылка должна быть публично доступной http(s)."
+    "One": "Загруженный файл хранится на сервере и подставляется при сборке; вставьте публичную http(s)-ссылку."
+  },
+  "BrandingPublicOriginMissingTitle": {
+    "One": "Картинки не подключатся к сборке"
+  },
+  "BrandingPublicOriginMissing": {
+    "One": "Публичный API-адрес (public API server) не задан. Загруженные картинки не будут использоваться в сборках: значения /upload/… невозможно преобразовать в публичную ссылку. Задайте переменную RUSTDESK_API_RUSTDESK_PUBLIC_API_SERVER в окружении API."
   },
   "AppLogo": {
     "One": "Логотип приложения (PNG)"
@@ -851,22 +863,22 @@
     "One": "Экран приватности (PNG)"
   },
   "ImageFieldNoteIcon": {
-    "One": "Требуется: PNG, квадрат; оптимально 256×256 (минимум 16×16)"
+    "One": "PNG · квадрат · 256×256 лучше всего · файл ≤5 МБ · ссылка ≤10 МБ"
   },
   "ImageFieldNoteLogo": {
-    "One": "Требуется: PNG; оптимально ≤300×60 — рендер не шире"
+    "One": "PNG · ≤300×60 · файл ≤5 МБ · ссылка ≤10 МБ"
   },
   "ImageFieldNoteScreen": {
-    "One": "Требуется: PNG (показ на весь экран)"
+    "One": "PNG · по всему экрану · файл ≤5 МБ · ссылка ≤20 МБ"
   },
   "ImageRangeIcon": {
-    "One": "Допустимо: квадрат 16×16–4096×4096; больше 256×256 ужимается до 256 для иконок Windows; файл ≤5 МБ, ссылка ≤10 МБ"
+    "One": "Допустимо: квадрат 16×16–4096×4096; квадрат больше 256 ужимается до 256 для значков Windows"
   },
   "ImageRangeLogo": {
-    "One": "Допустимо: PNG до 4096×4096; файл ≤5 МБ, ссылка ≤10 МБ"
+    "One": "Допустимый источник: PNG до 4096×4096"
   },
   "ImageRangeScreen": {
-    "One": "Допустимо: PNG до 4096×4096; файл ≤5 МБ, ссылка ≤20 МБ"
+    "One": "Допустимый источник: PNG до 4096×4096"
   },
   "ImageFieldPngOnlyError": {
     "One": "Допускаются только изображения PNG"
diff --git a/admin-ui/src/utils/i18n/zh_CN.json b/admin-ui/src/utils/i18n/zh_CN.json
index 382706b..871c6f2 100644
--- a/admin-ui/src/utils/i18n/zh_CN.json
+++ b/admin-ui/src/utils/i18n/zh_CN.json
@@ -843,10 +843,10 @@
     "One": "应用图标 (PNG)"
   },
   "ImageAttachFileButton": {
-    "One": "上传文件（≤5 MB）"
+    "One": "上传文件"
   },
   "ImageAttachLinkPlaceholder": {
-    "One": "或粘贴 http(s)…"
+    "One": "或粘贴 http(s) 链接…"
   },
   "ImageAttachClear": {
     "One": "清除"
@@ -854,8 +854,20 @@
   "ImageAttachPreviewEmpty": {
     "One": "无预览"
   },
+  "ImageUnavailable": {
+    "One": "文件不可用"
+  },
+  "ImageUnavailableDetails": {
+    "One": "无法加载——文件可能已不在服务器上；带此链接的构建将在 branding 阶段失败。"
+  },
   "BrandingImagesMechanicsNote": {
-    "One": "文件保存到服务器；构建时会根据 API 服务器地址自动解析链接。粘贴的链接必须是公网可访问的 http(s) 地址。"
+    "One": "上传的文件存储在服务器上，并在构建时解析；请粘贴可公网访问的 http(s) 链接。"
+  },
+  "BrandingPublicOriginMissingTitle": {
+    "One": "图片无法接入构建"
+  },
+  "BrandingPublicOriginMissing": {
+    "One": "未设置公开 API 服务器地址。上传的图片将无法在构建中使用：/upload/… 值无法转换为公开链接。请在 API 环境中设置 RUSTDESK_API_RUSTDESK_PUBLIC_API_SERVER 变量。"
   },
   "AppLogo": {
     "One": "应用 Logo (PNG)"
@@ -864,22 +876,22 @@
     "One": "隐私屏幕 (PNG)"
   },
   "ImageFieldNoteIcon": {
-    "One": "要求：PNG，正方形；建议 256×256（最小 16×16）"
+    "One": "PNG · 正方形 · 建议 256×256 · 文件 ≤5 MB · 链接 ≤10 MB"
   },
   "ImageFieldNoteLogo": {
-    "One": "要求：PNG；建议 ≤300×60（渲染不超过此宽度）"
+    "One": "PNG · ≤300×60 · 文件 ≤5 MB · 链接 ≤10 MB"
   },
   "ImageFieldNoteScreen": {
-    "One": "要求：PNG（全屏显示）"
+    "One": "PNG · 全屏 · 文件 ≤5 MB · 链接 ≤20 MB"
   },
   "ImageRangeIcon": {
-    "One": "允许：正方形 16×16–4096×4096；大于 256×256 会缩至 256 用作 Windows 图标；文件 ≤5 MB，链接 ≤10 MB"
+    "One": "允许：正方形 16×16–4096×4096；大于 256 的正方形会缩至 256 用作 Windows 图标"
   },
   "ImageRangeLogo": {
-    "One": "允许：PNG 最大 4096×4096；文件 ≤5 MB，链接 ≤10 MB"
+    "One": "允许来源：不超过 4096×4096 的 PNG"
   },
   "ImageRangeScreen": {
-    "One": "允许：PNG 最大 4096×4096；文件 ≤5 MB，链接 ≤20 MB"
+    "One": "允许来源：不超过 4096×4096 的 PNG"
   },
   "ImageFieldPngOnlyError": {
     "One": "仅支持 PNG 图片"
diff --git a/admin-ui/src/views/custom-client/index.vue b/admin-ui/src/views/custom-client/index.vue
index b307340..a7ef98d 100644
--- a/admin-ui/src/views/custom-client/index.vue
+++ b/admin-ui/src/views/custom-client/index.vue
@@ -491,6 +491,15 @@
 
         <el-divider content-position="left">{{ T('Branding') }}</el-divider>
         <p class="branding-mechanics-note">{{ T('BrandingImagesMechanicsNote') }}</p>
+        <el-alert
+          v-if="publicApiServerMissing"
+          type="warning"
+          :closable="false"
+          :title="T('BrandingPublicOriginMissingTitle')"
+          class="branding-public-origin-alert"
+        >
+          {{ T('BrandingPublicOriginMissing') }}
+        </el-alert>
         <el-row :gutter="20">
           <el-col :span="8">
             <el-form-item :label="T('AppIcon')" prop="app_icon_url" :error="serverFieldError('app_icon_url') || undefined">
@@ -505,6 +514,8 @@
                 :link-placeholder="T('ImageAttachLinkPlaceholder')"
                 :clear-label="T('ImageAttachClear')"
                 :preview-empty-label="T('ImageAttachPreviewEmpty')"
+                :unavailable-label="T('ImageUnavailable')"
+                :unavailable-details="T('ImageUnavailableDetails')"
                 :range-hint="T('ImageRangeIcon')"
                 :note-text="T('ImageFieldNoteIcon')"
                 @input="clearFieldError('app_icon_url')"
@@ -527,6 +538,8 @@
                 :link-placeholder="T('ImageAttachLinkPlaceholder')"
                 :clear-label="T('ImageAttachClear')"
                 :preview-empty-label="T('ImageAttachPreviewEmpty')"
+                :unavailable-label="T('ImageUnavailable')"
+                :unavailable-details="T('ImageUnavailableDetails')"
                 :range-hint="T('ImageRangeLogo')"
                 :note-text="T('ImageFieldNoteLogo')"
                 @input="clearFieldError('app_logo_url')"
@@ -549,6 +562,8 @@
                 :link-placeholder="T('ImageAttachLinkPlaceholder')"
                 :clear-label="T('ImageAttachClear')"
                 :preview-empty-label="T('ImageAttachPreviewEmpty')"
+                :unavailable-label="T('ImageUnavailable')"
+                :unavailable-details="T('ImageUnavailableDetails')"
                 :range-hint="T('ImageRangeScreen')"
                 :note-text="T('ImageFieldNoteScreen')"
                 @input="clearFieldError('privacy_screen_url')"
@@ -1500,6 +1515,14 @@ export default defineComponent({
       }
     }
 
+    // Whether the deployment config carries public_api_server (resolved by
+    // loadConfig). Starts false (configuration unknown — no banner) and only
+    // turns true on a successful config response without a public API address,
+    // which drives the single informational banner in the branding-images
+    // section: without a resolvable public origin, uploaded /upload/... values
+    // cannot become public build links.
+    const publicApiServerMissing = ref(false)
+
     const loadPresetIntoForm = async (preset) => {
       if (!preset) return
       try {
@@ -1758,6 +1781,7 @@ export default defineComponent({
           // internal/Docker address). key stays operational-only.
           // applyServerConfigDefaults semantics are unchanged.
           const cfg = res.data
+          publicApiServerMissing.value = !cfg.public_api_server
           Object.assign(serverConfigDefaults, {
             server_ip: cfg.public_id_server || cfg.id_server || '',
             key: cfg.key || '',
@@ -1789,6 +1813,7 @@ export default defineComponent({
       form, formRef, rules, builds, buildHistoryStatus, loading, submitting, downloadingBuildId, versionsState, versionsReady, productionPlatformReady,
       page, pageSize, total, versions,
       versionsError,
+      publicApiServerMissing,
        submitBuild, deleteBuild, resetForm, downloadBuild,
        statusType, statusLabel, T,
         presets, selectedPresetId, selectedPreset, presetSelectRef, onPresetSelect, saveCurrentAsPreset, deletePreset, uploadImage,
@@ -1947,6 +1972,12 @@ export default defineComponent({
   color: var(--el-text-color-secondary);
 }
 
+// Single informational banner for a deployment without a public API server —
+// warning, never an error state; the branding image fields stay usable.
+.branding-public-origin-alert {
+  margin-bottom: 12px;
+}
+
 .local-address-note {
   margin: 0 0 12px;
   color: var(--el-text-color-secondary);
diff --git a/admin-ui/tests/custom-client-validation.test.mjs b/admin-ui/tests/custom-client-validation.test.mjs
index 6e290d3..0c0bbdd 100644
--- a/admin-ui/tests/custom-client-validation.test.mjs
+++ b/admin-ui/tests/custom-client-validation.test.mjs
@@ -1371,3 +1371,33 @@ test('unmount invalidates the picker request through the shared lifecycleGuard',
   assert.equal(ctx.api.localAddressPicker.addresses.length, 0)
   assert.equal(ctx.api.localAddressPicker.loading, true) // nothing may write for a disposed component
 })
+
+// --- ImageAttachField preview label ---
+test('ImageAttachField preview label names the failed load via the local ref', () => {
+  // Regression: previewAriaLabel read props.previewFailed (never a declared
+  // prop, so always undefined) instead of the local ref, so the preview
+  // wrapper kept no aria-label in the failed state; the inner chip's own label
+  // only partly masked it. Exercise the component's real script slice.
+  const fieldSfc = readFileSync(new URL('../src/components/ui/ImageAttachField.vue', import.meta.url), 'utf8')
+  assert.equal(fieldSfc.includes('props.previewFailed ?'), false,
+    'the computed must read the local previewFailed ref, not a nonexistent prop')
+  const slice = (start, end) => {
+    assert.ok(fieldSfc.includes(start) && fieldSfc.includes(end), `missing ImageAttachField boundary: ${start}`)
+    return fieldSfc.slice(fieldSfc.indexOf(start), fieldSfc.indexOf(end, fieldSfc.indexOf(start)))
+  }
+  const props = reactive({ modelValue: '/upload/old.png', previewEmptyLabel: 'NoPreview', unavailableLabel: 'Unavailable' })
+  const context = { ref, computed, watch, props }
+  vm.createContext(context)
+  vm.runInContext(slice('const previewFailed = ref(false)', '\nconst clear =') + `
+    globalThis.api = { previewAriaLabel, previewFailed };
+  `, context)
+  const { api } = context
+  // A loaded preview carries no wrapper label; the img itself renders the value.
+  assert.equal(api.previewAriaLabel.value, undefined)
+  // A failed load must name the unavailable state on the wrapper itself.
+  api.previewFailed.value = true
+  assert.equal(api.previewAriaLabel.value, 'Unavailable')
+  // An empty field returns to the neutral no-preview label.
+  props.modelValue = ''
+  assert.equal(api.previewAriaLabel.value, 'NoPreview')
+})
diff --git a/docker/docker-compose.yml b/docker/docker-compose.yml
index 12e8fd7..3be2bf3 100644
--- a/docker/docker-compose.yml
+++ b/docker/docker-compose.yml
@@ -45,6 +45,11 @@ services:
     volumes:
       - ../data/server:/data
       - ../data/api:/app/data
+      # Persist API-uploaded public assets across image rebuilds. The only
+      # resources-path/public writer is the admin upload handler
+      # (api/http/controller/admin/file.go -> public/upload/<YYYYMMDD>/),
+      # served back at GET /upload/ (api/http/router/api.go:104).
+      - ../data/uploads:/app/resources/public/upload
       - rdgen-data:/rdgen-data
     networks:
       - rustdesk-net