Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/515ee7f2b93d4ded09b9fb3bcba1f634.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563