Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/73bd87c0eef8e8cead75b7dd8eb4fb6f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563