Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/c8b20fb84ffc9e2d5b113a1253ad2b4d.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563