I solved my problem by editing the bg-header.gif. Actually, I made a bg-header.jpg including the header background and the photo.
Thank you for this helping thread. I uploaded a header.jpg with (904px x 155px) and changed the style.css as Esmi adviced. I worked perfectly, so far.
Comparing http://cornelib.wordpress.com/ (to be the test installation) and http://verdensrommet.org/ (to be the live installation), I am missing the white edges around the image. Can anyone help me to work it out?
Thank you so much in advance!
