Its not a web server. Dansguardian is a content filter that works with squid to filter the contents in a web page. Now when it finds some unnecessary words that are banned in configuration it just shows ACCESS DENIED message to the client. That page is html page and is located in /etc/dansguardian/languages/ukenglish and the html file is called template.html.
I now want to edit it some how to show the logo of the organization on the Access denied page.
I first tried this
<img src="logo.jgp" />
But that did not work out. I do not know why and I want to know that. It should have as acid_kewpie said
relative paths ARE http links implicitly...