Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2175c26d30e6d6e1b4e9d51c25a97a0e.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563