Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b6d5ee9b7aba5d255ff3fc20dd36ad46.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563