如何生成yii2验证码和验证码？

public function actions()
{
    return [
        'captcha' => [
            'class' => 'yii\captcha\CaptchaAction',
            'fixedVerifyCode' => YII_ENV_TEST ? 'testme' : null,
        ],
    ];
}

use yii\captcha\Captcha;

// ...

<?= $form->field($model, 'verifyCode')->widget(Captcha::className(), [
    'captchaAction' => 'site/captcha',
    'template' => '<div class="row"><div class="col-lg-3">{image}</div><div class="col-lg-6">{input}</div></div>',
]) ?>

use yii\captcha\CaptchaValidator;

// ...

public function actionLogin()
{
    $model = new LoginForm();

    if ($model->load(Yii::$app->request->post()) && $model->login()) {
        // 登录成功
        return $this->goBack();
    }

    // 验证码验证
    $model->validateCaptcha();

    return $this->render('login', [
        'model' => $model,
    ]);
}