WordPress 3.0 added the ability for themes to easily allow custom headers. Users could pick one that the theme shipped with, or upload their own. But what if you run a branded multisite instance where you don’t want your users to be able to upload their own, but you still want them to easily be able to pick one? Now in WordPress 3.1, you can do just that.
So how do we do this?
Just paste the following code in your theme (or child theme) functions.php file.
[php]add_action(‘init’, ‘jorbin_remove_custom_header_uploads’, 11);
remove_theme_support( ‘custom-header-uploads’ );
If that’s not easy enough, check out The remove custom header uploads plugin in the WordPress plugin directory