General Support: Captcha Image Not Showing

Hi, I am trying to get captcha to work, because I am getting too much spam now and I have added this code to /themes/default/comments.php

<p>
<input type="text" name="url" id="url" value="" size="28" tabindex="3" />
<label for="url">Your Website (optional)</label>
</p>
<?php plogger_require_captcha(); ?>
<p>
<img src="'.$config["gallery_url"].'plog-captcha.php" alt="CAPTCHA Image" id="captcha-image" />
</p>
<p>
<input type="text" name="captcha" id="captcha" value="" size="28" tabindex="3" />
<label for="url">' . plog_tr('What does this say') . '?</label>
</p>
<p>
<label for="comment">Your Comment</label>
<br /><textarea name="comment" id="comment" cols="60" rows="4" tabindex="4"></textarea>
</p>

But the image won't show, it just shows the alt text instead

Please can someone help as I need to stop these spammers

Thanks

Anyone?