Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b6b034b6cd4f5904d806d3f5ce0c29c4.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563