Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/68b5e8096a754a68fc35f73f1ef3afe6.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563