Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a6ca4312ae279de6a8ed8b6c4bf336c4.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563