Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f7ce966455eed6a6a2b9e57b1c2df9bc.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563