There is a global variable called $pagenow for the use within WP Admin:
global $pagenow;
if ( $pagenow == 'upload.php') :
function custom_admin_notice() {
echo '<div class="updated"><p>Updated!</p></div>';
}
add_action( 'admin_notices', 'custom_admin_notice' );
endif;
UPDATE: Simply include the snippet in your themes or plugins functions.php
;