Read/get the image url in CaptchaBundle

[engharb]

I have added

->add('captcha', CaptchaType::class, array(
'as_url' => true,
'keep_value' => true,
'background_color' => array(255,255,255),
'width' => 200,
'height' => 50,
'length' => 5,
'label' => false,
'required' => true,
'label_attr' => array('class' => 'control-label'),
'attr' => array('class' => 'form-control', 'size' => 20, 'maxlength' => 6, 'style' => 'margin-bottom: 1em; margin-top: 1em;'),
))

into my form builder, but I can not load the image because I dont know the right URL that should be supported to my template/form.

Here is my front-end page:

">

            <div class="col-md-8">
               
                <img border="0" style="margin-bottom: 0.2em" title="captcha" alt="Captcha"
                     src="??????"/><br/>

                <?php echo $view['form']->row($form['captchaid']) ?>
                <?php echo $view['form']->widget($form['captcha']) ?>
                <?php echo $view['form']->errors($form['captcha']) ?>
            </div>
            <br/><br/>
        </div>

My question how to load/find the image url where my routing.yml:

gregwar_captcha_routing:
resource: "@GregwarCaptchaBundle/Resources/config/routing/routing.yml"
prefix: /_gcb