Should I throw a 404 to a request like /photo.php?id=123 if photo #123 does not exist?

The script will be called from a URL like example.com/photo.php?id=123 or example.com/photos/123 depending on if the have the pretty URLs featured enabled.

If photo #123 does not exist, a request to example.com/photos/123 should throw a 404 error. But, what about example.com/photo.php?id=123?