diff --git a/internal/captcha/dwelling_captcha.go b/internal/captcha/dwelling_captcha.go
index 304f42f..59055db 100644
--- a/internal/captcha/dwelling_captcha.go
+++ b/internal/captcha/dwelling_captcha.go
@@ -25,7 +25,7 @@ func NewDwellingCaptcha(expiry time.Duration) *DwellingCaptcha {
 			ExpireIn: ExpiryDate(expiry)}}
 }
 
-func (c *DwellingCaptcha) GenerateImage() *image.Image {
+func (c *DwellingCaptcha) generateImage() *image.Image {
 	ctx := gg.NewContext(dwImageWidth, dwImageHeight)
 
 	// fill background
@@ -67,7 +67,7 @@ func (c *DwellingCaptcha) GenerateImage() *image.Image {
 
 func (c *DwellingCaptcha) GetImage() *image.Image {
 	if c.Image == nil {
-		return c.GenerateImage()
+		return c.generateImage()
 	}
 
 	return &c.Image