Hi there.
Piwigo overrides the displays_errors directive from the /etc/php/php.ini. If You want to disable it go to the include folder in Your Piwigo installation and edit (as root) file common.inc.php.
Find the line:
@ini_set('display_errors', true);
and edit it so that it reads
@ini_set('display_errors', false);
and restart Your httpd service.
Cheers.
Andrzej