Hi Amalia,
This is wordpress code, so I think you’d need to put it in your header php, but also include <style> tags…but I could be wrong….
< ?php if (is_front_page()) {
?>
<style type="text/css">
body {
background:url (link2yourimage.jpg) !important;
}
</style>
< ?php } ?>
Mind you I think this is only going to use a fixed size image, so is probably not so nice, unless you are using a tile image.
Personally I think it might be better to use a plugin, to have a background that fits to individual screen size…..??