If you want to add a image to the header background you can do it by adding custom CSS. As you will see I created a different size image so that it will scale correctly on all displays without cropping.
#site-header {
background-image: url(images/volktoberfest-header-415.jpg);
}
@media (min-width: 700px) {
#site-header {
background-image: url(images/volktoberfest-header-812.jpg);
}
@media (min-width: 1024px) {
#site-header {
background-image: url(images/volktoberfest-header-1024.jpg);
}
}
@media (min-width: 1220px) {
#site-header {
background-image: url(images/volktoberfest-header-1220.jpg);
}