Image upload via Wysiwyg visibility front/back end

Question

Does anyone had an idea to how make an image visible on both side ?

Let me explain :

• I don't use any CMS
• I write with my own WYSIWYG
• My data folder is called DATA
• My back office folder is called ADMIN

There are my pages :

• index.php => Front page.
• ADMIN/index.php => Back page.
• data/images => Pictures folder

When I'm on the back office, I upload an image via a script. I can see my image on the WYSIWYG and his link are relative: ../data/images/1.jpg

Ahah? Yes, because when I'm on the front office, the link is wrong.

I don't want to replace (via str or whatever) the "../" when I'm saving my page or when I'm editing it.

I know there is a fu**ing easy idea, but can't find out.

Thanks! ;)