简单的字母验证码 php源代码

<?php
session_start();

// 生成随机验证码
function generateCaptcha($length = 6) {
    $characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
    $charactersLength = strlen($characters);
    $captcha = '';
    for ($i = 0; $i < $length; $i++) {
        $captcha .= $characters[rand(0, $charactersLength - 1)];
    }
    return $captcha;
}

// 设置验证码到session
$_SESSION['captcha'] = generateCaptcha();

// 创建图像
$image = imagecreatetruecolor(150, 50);
$backgroundColor = imagecolorallocate($image, 255, 255, 255);
$textColor = imagecolorallocate($image, 0, 0, 0);

imagefilledrectangle($image, 0, 0, 150, 50, $backgroundColor);
imagettftext($image, 20, 0, 20, 35, $textColor, 'arial.ttf', $_SESSION['captcha']);

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);
?>