第一步，在验证码上右击鼠标，在新标签页面查看图片，看一下页面是否有包什么错误异常。

第二步，如果页面显示500错误，参考常见问题中【500错误/请求出现错误】部分排查步骤。

在验证码上右击鼠标，在新标签页打开是以下信息

Whoops, looks like something went wrong.

1/1NotSupportedException in Driver.php line 19:GD Library extension not available with this PHP installation.

1. in Driver.php line 19

2. at Driver->__construct() in ImageManager.php line 112

3. at ImageManager->createDriver() in ImageManager.php line 68

4. at ImageManager->canvas('160', '46', '#ecf2f4') in Captcha.php line 241

5. at Captcha->create('default') in Facade.php line 215

6. at Facade::__callStatic('create', array('default')) in AuthController.php line 24

7. at AuthController->loginCaptcha()

8. at call_user_func_array(array(object(AuthController), 'loginCaptcha'), array()) in Controller.php line 256

9. at Controller->callAction('loginCaptcha', array()) in ControllerDispatcher.php line 164

10. at ControllerDispatcher->call(object(AuthController), object(Route), 'loginCaptcha') in ControllerDispatcher.php line 112

11. at ControllerDispatcher->Illuminate\Routing\{closure}(object(Request))

12. at call_user_func(object(Closure), object(Request)) in Pipeline.php line 139

13. at Pipeline->Illuminate\Pipeline\{closure}(object(Request))

缺少GD扩展库