diff --git a/file-upload-site/Dockerfile b/file-upload-site/Dockerfile
index 47ac341..2c37f8c 100644
--- a/file-upload-site/Dockerfile
+++ b/file-upload-site/Dockerfile
@@ -1,8 +1,8 @@
 FROM python:3.10-slim
 
-# 系统依赖（python-magic 需要 libmagic）
+# 系统依赖（python-magic 需要 libmagic，验证码需要清晰字体）
 RUN apt-get update && \
-    apt-get install -y --no-install-recommends libmagic1 && \
+    apt-get install -y --no-install-recommends libmagic1 fonts-dejavu-core && \
     rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app
diff --git a/file-upload-site/app.py b/file-upload-site/app.py
index 1350a28..040f9af 100644
--- a/file-upload-site/app.py
+++ b/file-upload-site/app.py
@@ -38,6 +38,16 @@ NAME_REGEX = re.compile(r'^[\u4e00-\u9fa5a-zA-Z0-9_]{2,20}$')
 # 文件名中不安全的字符
 UNSAFE_FILENAME_CHARS = re.compile(r'[<>:"/\\|?*\x00-\x1f]')
 
+# 验证码图片参数
+CAPTCHA_IMAGE_SIZE = (320, 100)
+CAPTCHA_FONT_SIZE = 68
+CAPTCHA_FONT_PATHS = (
+    "/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf",
+    "/usr/local/share/fonts/DejaVuSans-Bold.ttf",
+    "/System/Library/Fonts/Supplemental/Arial Bold.ttf",
+    "/System/Library/Fonts/Supplemental/Verdana Bold.ttf",
+)
+
 
 # ── 工具函数 ────────────────────────────────────────────────────────
 def sanitize_name(name: str) -> str | None:
@@ -88,9 +98,25 @@ def generate_captcha_text(length: int = 4) -> str:
     return ''.join(random.choices(chars, k=length))
 
 
+def load_captcha_font(size: int = CAPTCHA_FONT_SIZE) -> ImageFont.ImageFont:
+    """加载适合验证码的大号字体，兼容 Linux/Docker 和 macOS 本地环境"""
+    for font_path in CAPTCHA_FONT_PATHS:
+        if not os.path.exists(font_path):
+            continue
+        try:
+            return ImageFont.truetype(font_path, size)
+        except OSError:
+            continue
+
+    try:
+        return ImageFont.truetype("DejaVuSans-Bold.ttf", size)
+    except OSError:
+        return ImageFont.load_default(size=size)
+
+
 def generate_captcha_image(text: str) -> Image.Image:
     """生成验证码图片（含干扰线和噪点）"""
-    width, height = 320, 100
+    width, height = CAPTCHA_IMAGE_SIZE
     # 浅色随机背景
     bg_color = (random.randint(235, 255), random.randint(235, 255), random.randint(235, 255))
     image = Image.new('RGB', (width, height), bg_color)
@@ -109,15 +135,15 @@ def generate_captcha_image(text: str) -> Image.Image:
         dot_color = (random.randint(140, 200), random.randint(140, 200), random.randint(140, 200))
         draw.point((x, y), fill=dot_color)
 
-    # 绘制文字
-    try:
-        font = ImageFont.truetype("/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf", 65)
-    except OSError:
-        font = ImageFont.load_default()
+    font = load_captcha_font()
+    char_slot_width = width // len(text)
 
     for i, char in enumerate(text):
-        x = 20 + i * 72
-        y = random.randint(6, 18)
+        bbox = draw.textbbox((0, 0), char, font=font)
+        char_width = bbox[2] - bbox[0]
+        char_height = bbox[3] - bbox[1]
+        x = i * char_slot_width + (char_slot_width - char_width) // 2 - bbox[0] + random.randint(-4, 4)
+        y = (height - char_height) // 2 - bbox[1] + random.randint(-5, 5)
         color = (random.randint(0, 80), random.randint(0, 80), random.randint(0, 80))
         draw.text((x, y), char, font=font, fill=color)
 
diff --git a/file-upload-site/static/css/style.css b/file-upload-site/static/css/style.css
index ce57675..07be958 100644
--- a/file-upload-site/static/css/style.css
+++ b/file-upload-site/static/css/style.css
@@ -610,8 +610,11 @@ input[type="text"].input-error {
 }
 
 .modal-captcha-img {
-    height: 46px;
-    flex: 1;
+    height: 86px;
+    width: min(260px, 100%);
+    max-width: 260px;
+    min-width: 0;
+    flex: 1 1 0;
     border-radius: var(--radius-sm);
     border: 1.5px solid var(--border);
     cursor: pointer;
@@ -721,6 +724,11 @@ input[type="text"].input-error {
         height: 38px;
     }
 
+    .modal-captcha-img {
+        height: 72px;
+        max-width: 100%;
+    }
+
     .form-actions {
         flex-direction: column;
     }
diff --git a/file-upload-site/style.css b/file-upload-site/style.css
index 5b87e4e..07be958 100644
--- a/file-upload-site/style.css
+++ b/file-upload-site/style.css
@@ -610,9 +610,11 @@ input[type="text"].input-error {
 }
 
 .modal-captcha-img {
-    height: 80px;
-    width: 240px;
-    flex: none;
+    height: 86px;
+    width: min(260px, 100%);
+    max-width: 260px;
+    min-width: 0;
+    flex: 1 1 0;
     border-radius: var(--radius-sm);
     border: 1.5px solid var(--border);
     cursor: pointer;
@@ -722,6 +724,11 @@ input[type="text"].input-error {
         height: 38px;
     }
 
+    .modal-captcha-img {
+        height: 72px;
+        max-width: 100%;
+    }
+
     .form-actions {
         flex-direction: column;
     }