diff --git a/backend/app/services/captcha.py b/backend/app/services/captcha.py
index 07df890..c1f0bf4 100644
--- a/backend/app/services/captcha.py
+++ b/backend/app/services/captcha.py
@@ -4,10 +4,19 @@ import random
 import secrets
 import string
 import time
+from pathlib import Path
 
 from PIL import Image, ImageDraw, ImageFont
 
 CAPTCHA_TTL_SECONDS = 300
+CAPTCHA_WIDTH = 148
+CAPTCHA_HEIGHT = 48
+CAPTCHA_FONT_SIZE = 30
+CAPTCHA_FONT_PATHS = (
+    Path("/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf"),
+    Path("/System/Library/Fonts/SFNS.ttf"),
+    Path("/Library/Fonts/Arial Bold.ttf"),
+)
 _captchas: dict[str, tuple[str, float]] = {}
 
 
@@ -38,17 +47,29 @@ def clean_expired_captchas() -> None:
 
 
 def draw_captcha_image(code: str) -> str:
-    width, height = 132, 44
-    image = Image.new("RGB", (width, height), "#f8fafc")
+    image = Image.new("RGB", (CAPTCHA_WIDTH, CAPTCHA_HEIGHT), "#f8fafc")
     draw = ImageDraw.Draw(image)
-    font = ImageFont.load_default()
+    font = load_captcha_font()
     for i, char in enumerate(code):
-        draw.text((18 + i * 26, 13 + random.randint(-2, 2)), char, fill="#1f2937", font=font)
+        bounds = draw.textbbox((0, 0), char, font=font)
+        text_height = bounds[3] - bounds[1]
+        y = (CAPTCHA_HEIGHT - text_height) // 2 - bounds[1] + random.randint(-2, 2)
+        draw.text((12 + i * 33, y), char, fill="#111827", font=font)
     for _ in range(8):
-        x1, y1 = random.randint(0, width), random.randint(0, height)
-        x2, y2 = random.randint(0, width), random.randint(0, height)
+        x1, y1 = random.randint(0, CAPTCHA_WIDTH), random.randint(0, CAPTCHA_HEIGHT)
+        x2, y2 = random.randint(0, CAPTCHA_WIDTH), random.randint(0, CAPTCHA_HEIGHT)
         draw.line((x1, y1, x2, y2), fill="#cbd5e1", width=1)
 
     buffer = io.BytesIO()
     image.save(buffer, format="PNG")
     return "data:image/png;base64," + base64.b64encode(buffer.getvalue()).decode("ascii")
+
+
+def load_captcha_font() -> ImageFont.FreeTypeFont | ImageFont.ImageFont:
+    for path in CAPTCHA_FONT_PATHS:
+        if path.exists():
+            return ImageFont.truetype(str(path), CAPTCHA_FONT_SIZE)
+    try:
+        return ImageFont.load_default(size=CAPTCHA_FONT_SIZE)
+    except TypeError:
+        return ImageFont.load_default()
diff --git a/backend/tests/test_captcha.py b/backend/tests/test_captcha.py
index 88901c1..5ed8d7c 100644
--- a/backend/tests/test_captcha.py
+++ b/backend/tests/test_captcha.py
@@ -1,4 +1,16 @@
-from app.services.captcha import make_captcha, verify_captcha
+import base64
+import io
+
+from PIL import Image
+
+from app.services.captcha import (
+    CAPTCHA_FONT_SIZE,
+    CAPTCHA_HEIGHT,
+    CAPTCHA_WIDTH,
+    load_captcha_font,
+    make_captcha,
+    verify_captcha,
+)
 
 
 def test_captcha_can_only_be_used_once():
@@ -7,3 +19,12 @@ def test_captcha_can_only_be_used_once():
     # The real code is intentionally not exposed. This test locks in one-time consumption behavior.
     assert not verify_captcha(captcha_id, "bad")
     assert not verify_captcha(captcha_id, "bad")
+
+
+def test_captcha_uses_large_font_and_expected_image_size():
+    captcha = make_captcha()
+    encoded_image = captcha["image"].split(",", 1)[1]
+    image = Image.open(io.BytesIO(base64.b64decode(encoded_image)))
+
+    assert image.size == (CAPTCHA_WIDTH, CAPTCHA_HEIGHT)
+    assert getattr(load_captcha_font(), "size", CAPTCHA_FONT_SIZE) == CAPTCHA_FONT_SIZE
diff --git a/frontend/src/views/CertificateQuery.vue b/frontend/src/views/CertificateQuery.vue
index 869d44b..47dd2cd 100644
--- a/frontend/src/views/CertificateQuery.vue
+++ b/frontend/src/views/CertificateQuery.vue
@@ -409,7 +409,7 @@ h1 {
 
 .captcha-row {
   display: grid;
-  grid-template-columns: 1fr 132px;
+  grid-template-columns: minmax(0, 1fr) 148px;
   gap: 10px;
   width: 100%;
 }
@@ -422,7 +422,7 @@ h1 {
 }
 
 .captcha-button {
-  height: 34px;
+  height: 42px;
   padding: 0;
   border: 1px solid #dbe6ea;
   border-radius: 8px;