Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/cfd1dc5edb6d57a7ba33f67d0ab3e2e2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563