
i found this at http://www.phpcaptcha.org all i have done is intergrate it into usebb

FILE CHANGES
open your_template_folder/various.tpl.php
find
<tr>
<td class="fieldtitle">{l_PasswordAgain}</td><td>{passwd2_input}</td>
</tr>
add after
<tr>
<td class="fieldtitle">CAPCHA</td><td>{capcha}</td>
</tr>
open sources/panel_register.php
find
'passwd2_input' => '<input type="password" name="passwd2" size="25" maxlength="255" />',
add after
'capcha' => '<input type="text" name="code" size="25" maxlength="255" /> <img src="sources/capcha/securimage_show.php" />'',
FILE UPLOADS
Then upload this file to your sources folder
http://rapidshare.com/files/295450537/capcha.zip.html
if you haveny problms pm me



:S