Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/15d811b8f25016c2f98b7de806075ad0.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563