./includes/functions/form.php

<?php

if ( !defined('IN_SITE'))
{
    report ('Hacking attempt.', 'Insite unset');
}

function upload_single ($file, $id)
{
    if(is_uploaded_file($file[tmp_name]))
    {
        $extension = pathinfo($file['name']);
        $extension = $extension['extension'];
        move_uploaded_file($file[tmp_name], 'images/books/'.$file[name]);

        $newimagename = 'images/books/'.$id.'.'.$extension;
        rename('images/books/'.$file[name], $newimagename);
    }
}