如何使用PHP生成验证码图片

<?php
$width = 120; // 验证码图片的宽度
$height = 40; // 验证码图片的高度
$characters = 4; // 验证码字符个数

$possibleChars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';

$image = imagecreatetruecolor($width, $height);

$backgroundColor = imagecolorallocate($image, 255, 255, 255); // 背景颜色为白色
$textColor = imagecolorallocate($image, 0, 0, 0); // 文字颜色为黑色

imagefill($image, 0, 0, $backgroundColor);

$font = 'path/to/your/font.ttf'; // 字体文件路径，可以根据自己的需求修改

$captcha = '';

for ($i = 0; $i < $characters; $i++) {
    $randomChar = $possibleChars[rand(0, strlen($possibleChars) - 1)];
    $captcha .= $randomChar;

    $x = ($width / $characters) * $i + 10; // 10为字体边距
    $y = $height / 2 + 15; // 15为字体居中偏移量

    imagettftext($image, 20, 0, $x, $y, $textColor, $font, $randomChar);
}

session_start();
$_SESSION['captcha'] = $captcha;

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