Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/ded2b5ac7ea89dd129b81565e5e3f2bd.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563