CCaptcha

public static function checkRequirements($extension=null)
{
    if(extension_loaded('imagick'))
    {
        $imagick=new Imagick();
        $imagickFormats=$imagick->queryFormats('PNG');
    }
    if(extension_loaded('gd'))
    {
        $gdInfo=gd_info();
    }
    if($extension===null)
    {
        if(isset($imagickFormats) && in_array('PNG',$imagickFormats))
            return true;
        if(isset($gdInfo) && $gdInfo['FreeType Support'])
            return true;
    }
    elseif($extension=='imagick' && isset($imagickFormats) && in_array('PNG',$imagickFormats))
        return true;
    elseif($extension=='gd' && isset($gdInfo) && $gdInfo['FreeType Support'])
        return true;
    return false;
}

public function registerClientScript()
{
    $cs=Yii::app()->clientScript;
    $id=$this->imageOptions['id'];
    $url=$this->getController()->createUrl($this->captchaAction,array(CCaptchaAction::REFRESH_GET_VAR=>true));

    $js="";
    if($this->showRefreshButton)
    {
        // reserve a place in the registered script so that any enclosing button js code appears after the captcha js
        $cs->registerScript('Yii.CCaptcha#'.$id,'// dummy');
        $label=$this->buttonLabel===null?Yii::t('yii','Get a new code'):$this->buttonLabel;
        $options=$this->buttonOptions;
        if(isset($options['id']))
            $buttonID=$options['id'];
        else
            $buttonID=$options['id']=$id.'_button';
        if($this->buttonType==='button')
            $html=CHtml::button($label, $options);
        else
            $html=CHtml::link($label, $url, $options);
        $js="jQuery('#$id').after(".CJSON::encode($html).");";
        $selector="#$buttonID";
    }

    if($this->clickableImage)
        $selector=isset($selector) ? "$selector, #$id" : "#$id";

    if(!isset($selector))
        return;

    $js.="
jQuery(document).on('click', '$selector', function(){
jQuery.ajax({
    url: ".CJSON::encode($url).",
    dataType: 'json',
    cache: false,
    success: function(data) {
        jQuery('#$id').attr('src', data['url']);
        jQuery('body').data('{$this->captchaAction}.hash', [data['hash1'], data['hash2']]);
    }
});
return false;
});
";
    $cs->registerScript('Yii.CCaptcha#'.$id,$js);
}

protected function renderImage()
{
    if(!isset($this->imageOptions['id']))
        $this->imageOptions['id']=$this->getId();

    $url=$this->getController()->createUrl($this->captchaAction,array('v'=>uniqid()));
    $alt=isset($this->imageOptions['alt'])?$this->imageOptions['alt']:'';
    echo CHtml::image($url,$alt,$this->imageOptions);
}

public function run()
{
    if(self::checkRequirements('imagick') || self::checkRequirements('gd'))
    {
        $this->renderImage();
        $this->registerClientScript();
    }
    else
        throw new CException(Yii::t('yii','GD with FreeType or ImageMagick PHP extensions are required.'));
}