Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b4e9d46c6bb9aa89b34f0a49f79eaa2f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563