File not found

I've noticed something really strange.

Here is a part of my header.php code :

Code:

<link rel="icon" href="<?php echo base_url();?>images/favicon-GRO.ico" />
<link rel="stylesheet" href="<?php echo base_url();?>css/style.css" />

And when I display the html source code from firefox I get

Code:

<link rel="icon" href="<my_base_url as declared in app.php>/images/favicon-GRO.ico" 
<link rel="stylesheet" href="<my_base_url as declared in app.php>/public/css/style.css" />

Why did I get "public" for my css and not my image ???