Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6d6d42f9a3f9903f5000e4430e8b823f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563