I'm using lastest k2 and Joomla 1.5.22 version,

 

Recently I 've move to a VPS and try to disable following function according to joomla "Security Checklist 2 - Hosting and Server Setup" :

disable_functions = show_source, system, shell_exec, passthru, exec, phpinfo, popen, proc_openafter disabling these function the image of articles wont upload with no error message.could you please let me know which function should not be disable for upload image in k2 and why is that?