Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/78a8880b52e3cf7bc802cb9e8f1ca6dd.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563