Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6c183b673dfc08b84a5b868c8c5b4f57.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563