Update
//--- Start Settings for CAPTCHA ---
http://www.4homepages.de/forum/index.php?topic=21028.0 ---
//--- config by mawenzi 31.03.2008 ---
$captcha_enable = 1; // or 0 disables it.
$captcha_enable_comments = 1; // or 0 disables it.
$captcha_enable_upload = 1; // or 0 disables it.
$captcha_enable_registration = 1; // or 0 disables it.
$captcha_enable_postcards = 1; // or 0 disables it.
$captcha_path = './captcha'; // Path to the folder which contains the CAPTCHA files (backgrounds, fonts).
//$captcha_chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; // default
//$captcha_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; // also possible
$captcha_chars = "123456789";
$captcha_length = 5; // Number of letters of the CAPTCHA strings. Default value is 5.
$captcha_wordfile = 0; // If this option is set to 1, a word from "captcha/words.txt" is used. Default value is 0.
$captcha_width = 135; // Width of the CAPTCHA image in pixel. Default value is 200.
$captcha_height = 35; // Height of the CAPTCHA image in pixel. Default value is 70.
$captcha_text_color = "#ffffff"; // Color (Hex) of the CAPTCHA text. Default value is "#000000" (black).
$captcha_text_size = 14; // Size of the CAPTCHA text. Default value is 25.
$captcha_text_transparency = 100; // Transparency of the CAPTCHA text. Default value is 60.
$captcha_filter_text = 0; // If this option is set to 1, the CAPTCHA fonts will be filtered ("obscured"). Default value is 1.
$captcha_filter_bg = 1; // If this option is set to 1, the CAPTCHA background image will be filtered ("obscured"). Default value is 1.
//--- End Settings for CAPTCHA ---
Schrift auf Weiß gesetzt, andere Schrift installiert, Schrift etwas größer gesetzt.