If that's the case, I think you'll find that
http://www.thuleab.dk/./mod/guestbook/img/female.gif
will resolve to
http://www.thuleab.dk/mod/guestbook/img/female.gif
If you want, try changing the path on the other guestbook to
/./annemariesalling/mod/guestbook/img/ip.gif
that way the path is the same as your own guestbook. From what I can see, the /. isn't required, but it also doesn't do any harm.