Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/3e9a799cc6eb6a02e93742f8c4c7b4ac.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563