Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/78b2f9fd73b5a6105d0a76e239cdd760.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563