diff --git a/ui/src/utils/auth.ts b/ui/src/utils/auth.ts
index 8a24b17..909971a 100644
--- a/ui/src/utils/auth.ts
+++ b/ui/src/utils/auth.ts
@@ -53,7 +53,7 @@ function getCaptchaSrc(): string {
 }
 
 function verifyCaptcha(value: string): boolean {
-    return captcha.value === value.replace(/\s*/g, '').toUpperCase()
+    return captcha.value.toLowerCase() === value.replace(/\s*/g, '').toLowerCase()
 }
 
 export { login, logout, getLoginStatus, getUser, getUsername, getCaptchaSrc, verifyCaptcha }
diff --git a/ui/src/utils/common.ts b/ui/src/utils/common.ts
index fd1182f..f6bb9c1 100644
--- a/ui/src/utils/common.ts
+++ b/ui/src/utils/common.ts
@@ -101,7 +101,7 @@ function randomColor(start: number, end: number): string {
 }
 
 function getCaptcha(width: number, high: number, num: number): Captcha {
-    const CHARTS = '23456789ABCDEFGHJKLMNPQRSTUVWXYZ'.split('')
+    const CHARTS = '23456789ABCDEFGHJKLMNPRSTUVWXYZabcdefghijklmnpqrstuvwxyz'.split('')
 
     const canvas = document.createElement('canvas')
     const ctx = canvas.getContext('2d') as CanvasRenderingContext2D