Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/7d63d3ca64ff0e86511f0389a9d7e5cd.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563