diff --git a/docs/authn/captcha.md b/docs/authn/captcha.md
index a9d54b26..684b8468 100644
--- a/docs/authn/captcha.md
+++ b/docs/authn/captcha.md
@@ -2,11 +2,12 @@
 
 验证码（CAPTCHA）是“Completely Automated Public Turing test to tell Computers and Humans Apart”（全自动区分计算机和人类的图灵测试）的缩写，是一种区分用户是计算机还是人的公共全自动程序。可以防止用户用特定程序暴力破解方式进行不断的登陆尝试。
 
-文本验证码
+<b>文本验证码</b>
 
 <img src="{{ "/images/authn/captcha_text.png" | prepend: site.baseurl }}?{{ site.time | date: "%Y%m%d%H%M" }}"  alt=""/>
 
-算术验证码
+<b>算术验证码</b>
+
 <img src="{{ "/images/authn/captcha_arithmetic.png" | prepend: site.baseurl }}?{{ site.time | date: "%Y%m%d%H%M" }}"  alt=""/>