CCaptchaAction

public function generateValidationHash($code)
{
    for($h=0,$i=strlen($code)-1;$i>=0;--$i)
        $h+=ord($code[$i]);
    return $h;
}

protected function generateVerifyCode()
{
    if($this->minLength > $this->maxLength)
        $this->maxLength = $this->minLength;
    if($this->minLength < 3)
        $this->minLength = 3;
    if($this->maxLength > 20)
        $this->maxLength = 20;
    $length = mt_rand($this->minLength,$this->maxLength);

    $letters = 'bcdfghjklmnpqrstvwxyz';
    $vowels = 'aeiou';
    $code = '';
    for($i = 0; $i < $length; ++$i)
    {
        if($i % 2 && mt_rand(0,10) > 2 || !($i % 2) && mt_rand(0,10) > 9)
            $code.=$vowels[mt_rand(0,4)];
        else
            $code.=$letters[mt_rand(0,20)];
    }

    return $code;
}

protected function getSessionKey()
{
    return self::SESSION_VAR_PREFIX . Yii::app()->getId() . '.' . $this->getController()->getUniqueId() . '.' . $this->getId();
}

public function getVerifyCode($regenerate=false)
{
    if($this->fixedVerifyCode !== null)
        return $this->fixedVerifyCode;

    $session = Yii::app()->session;
    $session->open();
    $name = $this->getSessionKey();
    if($session[$name] === null || $regenerate)
    {
        $session[$name] = $this->generateVerifyCode();
        $session[$name . 'count'] = 1;
    }
    return $session[$name];
}

protected function renderImage($code)
{
    if($this->backend===null && CCaptcha::checkRequirements('imagick') || $this->backend==='imagick')
        $this->renderImageImagick($code);
    else if($this->backend===null && CCaptcha::checkRequirements('gd') || $this->backend==='gd')
        $this->renderImageGD($code);
}

protected function renderImageGD($code)
{
    $image = imagecreatetruecolor($this->width,$this->height);

    $backColor = imagecolorallocate($image,
            (int)($this->backColor % 0x1000000 / 0x10000),
            (int)($this->backColor % 0x10000 / 0x100),
            $this->backColor % 0x100);
    imagefilledrectangle($image,0,0,$this->width,$this->height,$backColor);
    imagecolordeallocate($image,$backColor);

    if($this->transparent)
        imagecolortransparent($image,$backColor);

    $foreColor = imagecolorallocate($image,
            (int)($this->foreColor % 0x1000000 / 0x10000),
            (int)($this->foreColor % 0x10000 / 0x100),
            $this->foreColor % 0x100);

    if($this->fontFile === null)
        $this->fontFile = dirname(__FILE__).DIRECTORY_SEPARATOR.'SpicyRice.ttf';

    $length = strlen($code);
    $box = imagettfbbox(30,0,$this->fontFile,$code);
    $w = $box[4] - $box[0] + $this->offset * ($length - 1);
    $h = $box[1] - $box[5];
    $scale = min(($this->width - $this->padding * 2) / $w,($this->height - $this->padding * 2) / $h);
    $x = 10;
    $y = round($this->height * 27 / 40);
    for($i = 0; $i < $length; ++$i)
    {
        $fontSize = (int)(rand(26,32) * $scale * 0.8);
        $angle = rand(-10,10);
        $letter = $code[$i];
        $box = imagettftext($image,$fontSize,$angle,$x,$y,$foreColor,$this->fontFile,$letter);
        $x = $box[2] + $this->offset;
    }

    imagecolordeallocate($image,$foreColor);

    header('Pragma: public');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Content-Transfer-Encoding: binary');
    header("Content-Type: image/png");
    imagepng($image);
    imagedestroy($image);
}

protected function renderImageImagick($code)
{
    $backColor=$this->transparent ? new ImagickPixel('transparent') : new ImagickPixel(sprintf('#%06x',$this->backColor));
    $foreColor=new ImagickPixel(sprintf('#%06x',$this->foreColor));

    $image=new Imagick();
    $image->newImage($this->width,$this->height,$backColor);

    if($this->fontFile===null)
        $this->fontFile=dirname(__FILE__).DIRECTORY_SEPARATOR.'SpicyRice.ttf';

    $draw=new ImagickDraw();
    $draw->setFont($this->fontFile);
    $draw->setFontSize(30);
    $fontMetrics=$image->queryFontMetrics($draw,$code);

    $length=strlen($code);
    $w=(int)($fontMetrics['textWidth'])-8+$this->offset*($length-1);
    $h=(int)($fontMetrics['textHeight'])-8;
    $scale=min(($this->width-$this->padding*2)/$w,($this->height-$this->padding*2)/$h);
    $x=10;
    $y=round($this->height*27/40);
    for($i=0; $i<$length; ++$i)
    {
        $draw=new ImagickDraw();
        $draw->setFont($this->fontFile);
        $draw->setFontSize((int)(rand(26,32)*$scale*0.8));
        $draw->setFillColor($foreColor);
        $image->annotateImage($draw,$x,$y,rand(-10,10),$code[$i]);
        $fontMetrics=$image->queryFontMetrics($draw,$code[$i]);
        $x+=(int)($fontMetrics['textWidth'])+$this->offset;
    }

    header('Pragma: public');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Content-Transfer-Encoding: binary');
    header("Content-Type: image/png");
    $image->setImageFormat('png');
    echo $image->getImageBlob();
}

public function run()
{
    if(isset($_GET[self::REFRESH_GET_VAR]))  // AJAX request for regenerating code
    {
        $code=$this->getVerifyCode(true);
        echo CJSON::encode(array(
            'hash1'=>$this->generateValidationHash($code),
            'hash2'=>$this->generateValidationHash(strtolower($code)),
            // we add a random 'v' parameter so that FireFox can refresh the image
            // when src attribute of image tag is changed
            'url'=>$this->getController()->createUrl($this->getId(),array('v' => uniqid())),
        ));
    }
    else
        $this->renderImage($this->getVerifyCode());
    Yii::app()->end();
}

public function validate($input,$caseSensitive)
{
    $code = $this->getVerifyCode();
    $valid = $caseSensitive ? ($input === $code) : strcasecmp($input,$code)===0;
    $session = Yii::app()->session;
    $session->open();
    $name = $this->getSessionKey() . 'count';
    $session[$name] = $session[$name] + 1;
    if($session[$name] > $this->testLimit && $this->testLimit > 0)
        $this->getVerifyCode(true);
    return $valid;
}