Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6b91a33e8c1ea1a02d0dc3088807c477.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563