How to set a automatically base url?

[eluser]pbreit[/eluser]
Where is your images directory? Is it at the same level as your "/system/" directory?

Your directory structure should be something like:
/htdocs/codeigniter/
/htdocs/codeigniter/index.php
/htdocs/codeigniter/system/
/htdocs/codeigniter/images/
/htdocs/codeigniter/images/myimage.gif

Can you view your image in your browser just with the URL:
http://www.mysite.com/images/myimage.gif

Are you rewriting your URLs in an .htaccess file to get rid of the "index.php" in your URLs?

Also, you might try everything without <base> tags (which are generally unnecessary).

Finally, if you put your code in "code" tags, the forum software will not filter it and it will be easier to read.