Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/89f9d12815b7ecc00b0abc97f5c76f4b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563