Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/7dc0e553e72a848d9a6b1f46306c8fd8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563