laravel怎么加入验证码功能

"require": {
        "php": ">=5.5.9",
        "laravel/framework": "5.2.*",
        "gregwar/captcha": "1.*"
    },

// 验证码的路由
Route::get('captcha','Index\RegisterController@code');

/*
author:咔咔
address:陕西西安
wechat:fangkangfk
*/
// 验证码
    public function code()
    {
        $builder = new CaptchaBuilder();
        $builder->build(150,32);
        $phrase = $builder->getPhrase();
        //把内容存入session
        Session::flash('milkcaptcha', $phrase); //存储验证码
        ob_clean();
        return response($builder->output())->header('Content-type','image/jpeg');
    }

<img src="{{url('captcha')}}" style="width: 130px;height: 60px;margin-left: 410px;position: relative;top: -74px;" onclick="this.src=this.src+'?'+Math.random()" class="code" >