Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6e5c2bf63c8e305b9faf3f4b3ab32f3c.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563