PHP 驗證碼類別：支援干擾線、TTF 字型、Session 驗證

ImageCode 類別完整程式碼

<?php
class ImageCode {
    private $width, $height, $count, $disturbCode, $fontFile, $sessionCode;

    public function __construct($width=120, $height=40, $count=4, $disturbCode='ABCDEFGHJKLMNPQRSTUVWXYZ23456789', $fontFile='') {
        $this->width       = $width;
        $this->height      = $height;
        $this->count       = $count;
        $this->disturbCode = $disturbCode;
        $this->fontFile    = $fontFile ?: 'C:/Windows/Fonts/arial.ttf'; // 預設字型路徑
        $this->sessionCode = $this->generateCode();
        session_start();
        $_SESSION['verify_code'] = $this->sessionCode;
    }

    public function output() {
        $im = $this->createCanvas();
        $this->drawBackground($im);
        $this->drawDisturb($im);
        $this->drawCode($im);
        header("Content-Type: image/gif");
        imagegif($im);
        imagedestroy($im);
    }

    private function createCanvas() {
        return imagecreate($this->width, $this->height);
    }

    private function drawBackground($im) {
        $bg = imagecolorallocate($im, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));
        imagefill($im, 0, 0, $bg);
    }

    private function drawDisturb($im) {
        $lines = $this->height * 2;
        for ($i=0; $i<$lines; $i++) {
            $x = mt_rand(0, $this->width);
            $y = mt_rand(0, $this->height);
            $angle = mt_rand(0, 360);
            $size  = mt_rand(8, 15);
            $char  = $this->disturbCode[mt_rand(0, strlen($this->disturbCode)-1)];
            $color = imagecolorallocate($im, mt_rand(40,140), mt_rand(40,140), mt_rand(40,140));
            imagettftext($im, $size, $angle, $x, $y, $color, $this->fontFile, $char);
        }
    }

    private function drawCode($im) {
        $y = $this->height/2 + $this->height/4;
        $size = mt_rand(20, 30);
        for ($i=0; $i<$this->count; $i++) {
            $char = $this->sessionCode[$i];
            $x = ($this->width / $this->count) * $i + 8;
            $angle = mt_rand(-20, 20);
            $color = imagecolorallocate($im, mt_rand(0,50), mt_rand(50,100), mt_rand(100,140));
            imagettftext($im, $size, $angle, $x, $y, $color, $this->fontFile, $char);
        }
    }

    private function generateCode() {
        $code = '';
        $len  = strlen($this->disturbCode);
        for ($i=0; $i<$this->count; $i++) {
            $code .= $this->disturbCode[mt_rand(0, $len-1)];
        }
        return $code;
    }

    public static function verify($input) {
        session_start();
        return isset($_SESSION['verify_code']) && strtoupper($input) === strtoupper($_SESSION['verify_code']);
    }
}
?>

使用方式

1. 產生驗證碼圖片 (captcha.php)

<?php
require_once 'ImageCode.php';
header("Content-Type: image/gif");
$captcha = new ImageCode(130, 40, 4);
$captcha->output();

2. 表單驗證

<form action="check.php" method="post">
  驗證碼: <input name="code" />
  <img src="captcha.php" onclick="this.src='captcha.php?'+Math.random()" style="cursor:pointer" title="點擊更換"/>
  <input type="submit" />
</form>

3. 後端驗證 (check.php)

<?php
require_once 'ImageCode.php';
if (ImageCode::verify($_POST['code'])) {
    echo "驗證通過";
} else {
    echo "驗證碼錯誤";
}

部署注意事項

1. 字型檔案：Linux 伺服器需上傳 TTF 字型檔，並指定正確路徑
2. GD/FreeType：PHP 編譯需支援 --with-freetype-dir 才能使用 imagettftext()
3. Session 生命週期：驗證碼 Session 應設較短過期時間 (如 5-10 分鐘)
4. 安全性：生成的驗證碼儲存在 Session 而非 Cookie，防止客戶端竄改

現代化替代方案

• Google reCAPTCHA v3：無感驗證，依行為評分
• hCaptcha：隱私優先，支援中文
• Slider/Click 驗證：前端互動式，體驗更佳
• 後端速率限制：配合 Redis 限制 IP/帳號請求頻率，減少驗證碼彈出機率