Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/cb4bd661f2e7a4d5cf56cf94e8b31b6f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563