Customize the manual logout page

[guus77]

I have followed this link
http://forum.pfsense.org/index.php/topic,41845.0.html

in order to set a manual logout procedure in my captive portal and everything works fine.
Now I would like to customize the page http://xxx.xxx.xxx.xxx:8000/logout inserting a background image.
I have tried to modify this section of captiveportal.inc file

**_<title>{$g['product_name']}</title>

Click to redirecting for …

Click the button below to disconnect.

Note

You can now leave this page while surfing for easy make a logout,
In case of you lose this page just enter on browser address bar._**

but the image "bg-refresh.jpg" loaded in the folder "images" into /etc/inc is never displayed (even after restarting the captiveportal).

How can I do?
Thanx in advance for your help