Here is a plugin I copied/pasted together for a client with a similar wish.
Save the code as `zp-branding.php` and place it in the plugins folder.
Then activate the plugin.
`
<?php
$plugin_is_filter = 5|ADMIN_PLUGIN;
$plugin_description = gettext("Remove Zenphoto logo from the backend");
zp_register_filter('admin_head', 'zpBranding::customZpLogo');
class zpBranding {
static function customZpLogo() {
global $_zp_current_admin_obj,$_zp_admin_tab,$_zp_admin_subtab,$_zp_gallery;
if (zp_loggedin(ADMIN_RIGHTS)) {
?>
<script type="text/javascript">
// <!-- <![CDATA[
$(document).ready(function(){
$('#administration img#logo').css({'display':'none'});
});
// ]]> -->
</script>
<?php
}
}
}
?>
`