Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/428b2bbaf0e3602e4d05cd1f9de0d71c.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563