Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/5b387d29bfd4c17c97b9eb47a32e5900.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563