Yii2验证码如何脱离ActiveForm单独使用

//WebController
class WebController extends Controller {
    //引入验证码Action
    public function actions() {
        return [
            'captcha' => [
                'class' => 'yii\captcha\CaptchaAction',
                'maxLength' => 4,
                'minLength' => 4,
            ],
        ];
    }
}

<img id="verify_image" src="/web/captcha">

$('#verify_image').click(function () {
    $.get(
        "/web/captcha?refresh=1",{},function (data) {
            $('#verify_image').attr('src', data.url);
        },"json"
    );
});

{"hash1":466,"hash2":466,"url":"/wap/my/captcha?v=598d8247db06a"}

$verifycode = \Yii::$app->request->post('verify_code');
$verifycode2 = $this->createAction("captcha")->getVerifyCode(false);
if($verifycode != $verifycode2){
    //验证码错误
}