Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/d6b2c0d2b3f75a01afa32c2e5551f813.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563