Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/31c74d5d26665537fa39a5f1cc4cd82b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563