<?php 
    class VerificationCode{ 
        private $charset="abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ23456789";  //隨機因子 
        private $code;  //驗證碼 
        private $codelen=4; //驗證碼長度 
        private $width=110; //寬度 
        private $height=30; //高度 
        private $img;   //圖像資源句柄 
        private $font;  //制定字體 
        private $fontSize=25;   //字體大小 
        private $fontColor; //字體顏色 
        public function __construct(){ 
            $this->font="CALIBRIZ.TTF"; 
        } 
        //生成驗證碼 
        private function createCode(){ 
            $len=strlen($this->charset)-1; 
            for ($i = 0; $i < $this->codelen; $i++) { 
                $this->code .= $this->charset[mt_rand(0,$len)]; 
            } 
        } 
        //生成背景 
        private function createBg(){ 
            $this->img=imagecreatetruecolor($this->width,$this->height); 
            $color = imagecolorallocate($this->img,mt_rand(157,255),mt_rand(157,255),mt_rand(157,255)); 
            imagefilledrectangle($this->img,0,$this->height,$this->width,0,$color); 
        } 
        //生成文字 
        private function createFont(){ 
            $x=$this->width/$this->codelen; 
            for ($i = 0; $i < $this->codelen; $i++) { 
                $this->fontColor=imagecolorallocate($this->img,mt_rand(0,156),mt_rand(0,156),mt_rand(0,156)); 
                imagettftext($this->img,$this->fontSize,mt_rand(-30,30),$i*$x+mt_rand(1,5),$this->height/1.4,$this->fontColor,$this->font,$this->code[$i]);  // chabaoo.cn
                //imagestring($this->img,5,$i*$x+mt_rand(1,5),5,$this->code[$i],$this->fontColor); 
            } 
        } 
        //生成線條、雪花 
        private function createDisturb(){ 
            for ($i = 0; $i < 6; $i++) { 
                $color=imagecolorallocate($this->img,mt_rand(0,156),mt_rand(0,156),mt_rand(0,156)); 
                imageline($this->img,mt_rand(0,$this->width),mt_rand(0,$this->width),mt_rand(0,$this->width),mt_rand(0,$this->width),$color); 
            } 
            for ($i = 0; $i < 100; $i++) { 
                $color=imagecolorallocate($this->img,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255)); 
                imagestring($this->img,mt_rand(1,5),mt_rand(0,$this->width),mt_rand(0,$this->height),'*',$color); 
            } 
        } 
        //輸出 
        private function outPut(){ 
            header("Content-Type:image/png"); 
            imagepng($this->img); 
            imagedestroy($this->img); 
        } 
        public function showCode(){ 
            $this->createBg(); 
            $this->createCode(); 
            $this->createDisturb(); 
            $this->createFont(); 
            $this->outPut(); 
        } 
        //獲取驗證碼 
        public function getCode(){ 
            return strtolower($this->code); 
        } 
    } 
?>

<?php 
    session_start(); 
    require_once 'VerificationCode.class.php'; 
    $code=new VerificationCode(); 
    $_SESSION['code']=$code->getCode(); 
    $code->showCode(); 
?> 

驗證碼:<input type="text" name="code" /><img src="code.php" onclick="javascript:this.src='code.php?time='+Math.random();" />