public function actions() { 
return [ 
'captcha' => [ 
'class' => 'yii\captcha\CaptchaAction', 
'maxLength' => 4, 
'minLength' => 4 
], 
]; 
}

public function behaviors() { 
return [ 
'access' => [ 
'class' => AccessControl::className(), 
'rules' => [ 
[ 
'actions' => ['login', 'error', 'captcha'], 
'allow' => true, 
], 
], 
]; 
}

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

class LoginForm extends Model { 
//...... public $verifyCode; 
public function rules() { 
return [ 
//...... 
['verifyCode', 'captcha'], 
]; 
} 
public function attributeLabels() { 
return [
'verifyCode' => '', //验证码的名称，根据个人喜好设定 
]; 
} 
} 
//定义了verifyCode属性 
//rules规则添加了验证 
//label中定义了其显示名称 

$('验证码对象').click();