2시간 삽질해서 jQuery로 변경했습니다.

write.skin.php

259번째줄(basic 스킨)
<script type="text/javascript" src="<?="$g4[path]/js/prototype.js"?>"></script>
<script type="text/javascript">
function imageClick() {
    var url = "<?=$g4[bbs_path]?>/kcaptcha_session.php";
    var para = "";
    var myAjax = new Ajax.Request(
        url, 
        {
            method: 'post', 
            asynchronous: true,
            parameters: para, 
            onComplete: imageClickResult
        });
}

function imageClickResult(req) { 
    var result = req.responseText;
    var img = document.createElement("IMG");
    img.setAttribute("src", "<?=$g4[bbs_path]?>/kcaptcha_image.php?t=" + (new Date).getTime());
    document.getElementById('kcaptcha_image').src = img.getAttribute('src');

    md5_norobot_key = result;
}

<? if (!$is_member) { ?>Event.observe(window, "load", imageClick);<? } ?>


위 내용을
<script type="text/javascript">
//kcapcha jQuery 로 변경.
function imageClick() {
 $.ajax({
   type:"POST",
   url: "<?=$g4[bbs_path]?>/kcaptcha_session.php",
   success: function(req) { 
         var result = req;
      $("#kcaptcha_image").attr("src","<?=$g4[bbs_path]?>/kcaptcha_image.php?t=" + (new Date).getTime());        
         md5_norobot_key = result;
     }
 });
}
<? if (!$is_member) { ?>
$(function(){
 imageClick();
 $("#kcaptcha_image").click(function(){imageClick();});
});
<? } ?>

위와 같이 변경


viwe_comment.skin.php 파일 135번째줄

<script type="text/javascript">
//kcapcha jQuery 로 변경.
function imageClick() {
 $.ajax({
   type:"POST",
   url: "<?=$g4[bbs_path]?>/kcaptcha_session.php",
   success: function(req) { 
         var result = req;
      $("#kcaptcha_image").attr("src","<?=$g4[bbs_path]?>/kcaptcha_image.php?t=" + (new Date).getTime());        
         md5_norobot_key = result;
     }
 });
}
<? if (!$is_member) { ?>
$(function(){
 $("#kcaptcha_image").click(function(){imageClick();});
});
<? } ?>

위와 같이변경


jQuery 는 haed.sub.php 에 올려줘야 됩니다.