None of your links worked for me, so I downloaded it from the Wiki. The Readme there didn't work at all, but I figured it out. The files changed where you have to add the code. This is how I made it work:
1. Upload generate_image.php to the /zen folder, change the permisson on this file to 777 (allow write to everybody).
Upload code.png to the /zen/images folder
2. Open the image.php in the folder of your current theme.
Add `<? include('zen/generate_code.php');?>`
Add `<label for="code"><img src='/zenphoto/zen/images/code.png' alt="Code"/></label>` where you ant the picture with the Captcha to be, add `<input type="text" id="code" name="code" size="3" class="inputbox" /><input type="hidden" name="code_h" value="<? echo $code; ?>"/>`where you want the input box to be.
In the default theme this would mean to find
`<tr>
<td><label for="website">Site:</label></td>
<td><input type="text" id="website" name="website" size="40" value="<?php echo $stored[2];?>" class="inputbox" /></td>
</tr>`
and after this add
`<tr>
<? include('zen/generate_code.php');?>
<td><label for="code"><img src='/zenphoto/zen/images/code.png' alt="Code"/></label></td>
<td><input type="text" id="code" name="code" size="3" class="inputbox" /><input type="hidden" name="code_h" value="<? echo $code; ?>"/></td>
</tr>`
4. Open [b] /zen/functions-controller.php[/b]
Find the lines
` $commentadded = $_zp_current_image->addComment(strip_tags($_POST['name']), strip_tags($_POST['email']),
$website, kses($_POST['comment'], zp_conf('allowed_tags')));`
in the zp_handle_comment function.
Change this to
`$commentadded = $_zp_current_image->addComment(strip_tags($_POST['name']), strip_tags($_POST['email']), $website,
kses($_POST['comment'], zp_conf('allowed_tags'))`[b]`,strip_tags($_POST['code']),$_POST['code_h']);`[/b]
5. Open [b]/zen/class-image.php[/b]
Find the `function addComment($name, $email, $website, $comment) {`
and replace this line with `function addComment($name, $email, $website, $comment,$code,$code_ok) {`
A few lines further in this function you'll find ` $comment = trim($comment);`.
After this add [b]`$code = trim($code);
$code_ok = trim($code_ok);`[/b]
and replace ` if (empty($email) || !is_valid_email_zp($email) || empty($name) || empty($comment)) {`
with ` if (empty($email) || !is_valid_email_zp($email) || empty($name) || empty($comment) || (md5($code)<>$code_ok)) {`