Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/8b1d91edad8fd1d1cc1bf7c793b57e09.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563