Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/ac4d0c8611bb635c498d7e813e68c7c3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563