/*      *说明：函数功能是生成验证码     * 参数说明：输入 长度，宽度，高度     */    function vcode($_code_length = 4, $_width = 75, $_height = 25){                $_font=dirname(__FILE__).'/font/Elephant.ttf';//注意字体路径要写对，否则显示不了图片                $_fontsize=$_height/1.8;        $_nmsg="";        for($i=0;$i<$_code_length;$i++){            $_nmsg .= dechex(mt_rand(0,15));        }        if(!isset($_SESSION)){            session_start();        }                $_SESSION["vcode"] = $_nmsg;        $_img = imagecreatetruecolor($_width, $_height);        $_white = imagecolorallocate($_img, 250, 250, 250);        imagefill($_img, 0, 0, $_white);        $_gray = imagecolorallocate($_img, 196, 196, 196);        imagerectangle($_img, 0, 0, $_width-1, $_height-1, $_gray);        for ($i=0; $i < 6; $i++) {             $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));            imageline($_img, mt_rand(0,$_width), mt_rand(0, $_height),mt_rand(0,$_width), mt_rand(0, $_height), $_md_color);        }        for ($i=0; $i < 50; $i++) {             $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));            imagestring($_img, 1, mt_rand(1,$_width-5), mt_rand(1, $_height-5), "*", $_md_color);        }        for ($i=0; $i < $_code_length ; $i++) {             $_md_color = imagecolorallocate($_img, mt_rand(0,102), mt_rand(0,102), mt_rand(0,102));            //imagestring($_img, 5, $i * $_width/$_code_length+ mt_rand(1, 10), mt_rand(1, $_height/2), $_SESSION["vcode"][$i], $_md_color);            imagettftext($_img,$_fontsize,mt_rand(-20,20),$_fontsize*$i+mt_rand(1,5),$_height / 1.4,$_md_color,$_font,$_SESSION["vcode"][$i]);        }        header("Content-Type:image/png");        imagepng($_img);        imagedestroy($_img);    }