請參考前面提到的這篇文章, 並在 chinese_img 的目錄下頭, 再建立一個子目錄 backgrounds, 然後把你所要使用的背景圖案的 gif 檔案, 放到這個目錄下頭.

接著把 usercp_captcha_chinese.php 改成下面這個樣子:

<?php
 
if ( !defined('IN_PHPBB') )
{
        die('Hacking attempt');
        exit;
}
// Do we have an id? No, then just exit
if (empty($HTTP_GET_VARS['id']))
{
        exit;
}
 
$confirm_id = htmlspecialchars($HTTP_GET_VARS['id']);
 
if (!preg_match('/^[A-Za-z0-9]+$/', $confirm_id))
{
        $confirm_id = '';
}
 
$gd = true;
if(!extension_loaded("gd")){
        //Gd isn't loaded
        //Display error messages always, or not?
        $gd = false;
}
if(!function_exists("gd_info") || !function_exists('imagettftext')){
        //GD function, gd_info don't exists. GD isn't loaded correctly.
        //Freetype function imagettftext doesn't exists. This is required by this mod.
        $gd = false;
}
if($gd === false){
        //GD not loaded, or one of the needed functions aren't there. Require usercp_confirm ;)
        require($phpbb_root_path . 'includes/usercp_confirm.' . $phpEx);
        die;
}
 
// Try and grab code for this id and session
$sql = 'SELECT code
        FROM ' . CONFIRM_TABLE . "
        WHERE session_id = '" . $userdata['session_id'] . "'
                AND confirm_id = '$confirm_id'";
$result = $db->sql_query($sql);
 
// If we have a row then grab data else create a new id
if ($row = $db->sql_fetchrow($result))
{
        $db->sql_freeresult($result);
        $code = $row['code'];
}
else
{
        exit;
}
 
if (function_exists('ImageRotate'))
    $size = 36;
else
    $size = 24;
 
$bg_files = glob($phpbb_root_path.'includes/chinese_img/backgrounds/*.gif');
$bg_file = $bg_files[rand(0, count($bg_files)-1)];
 
$len = strlen($code);
$im = ImageCreate(24 * $len, 24);
$background = ImageColorAllocate($im, 255, 255, 255);
 
$im_bg = @ImageCreateFromGIF($bg_file);
if ($im_bg) {
    list($width, $height, $type, $attr) = @GetImageSize($bg_file);
    if (function_exists('ImageCopyReSampled'))
        ImageCopyReSampled($im, $im_bg, 0, 0, 0, 0, 24 * $len, 24, $width, $height);
    else
        ImageCopyReSized($im, $im_bg, 0, 0, 0, 0, 24 * $len, 24, $width, $height);
    ImageDestroy($im_bg);
}
 
for ($i = 0; $i < $len; $i++) {
    $im_num = @ImageCreateFromPNG($phpbb_root_path . 'includes/chinese_img/'.$code[$i].'.png');
    if (function_exists('ImageRotate')) {
        $im_rotate = ImageRotate($im_num, rand(-45, 45), 0);
        ImageDestroy($im_num);
        $im_num = ImageCreate($size, $size);
        if (function_exists('ImageCopyReSampled'))
            ImageCopyReSampled($im_num, $im_rotate, 0, 0, 0, 0, $size, $size, imagesx($im_rotate), imagesy($im_rotate));
        else
            ImageCopyReSized($im_num, $im_rotate, 0, 0, 0, 0, $size, $size, imagesx($im_rotate), imagesy($im_rotate));
        ImageDestroy($im_rotate);
    }
    if ($im_num) {
        ImageColorTransparent($im_num, ImageColorAt($im_num, 0, 0));
        ImageCopy($im, $im_num, 24 * $i, 0, 0, 0, 24, 24);
        ImageDestroy($im_num);
    }
}
 
header('content-type:image/png');
header('Cache-control: no-cache, no-store');
 
ImagePNG($im);
ImageDestroy($im);
die;
 
?>

這樣子就應該可以了.

對了, 如果你的系統產生的字並沒有旋轉, 表示你的系統的 PHP 不支援 ImageRotate() 這個函式 (例如 Debian 本身內建). 如果你一定要使用這個功能, 就必須自行編譯一份有含這個功能的 php gd 模組 (在 Debian 中, 把 rules 的

--with-gd=shared,/usr 

改成

--with-gd=shared 

重新編譯後, 把 gd.so 覆蓋原本的就可以了.