Attaching them is the best way and the preferred way...sometimes those image hosting sites will delete images that haven't been used or managed over a certain time frame...or sometimes they'll just delete them for no reason. By attaching them through the site, they stay with the site, thus making archived threads more a reality. Plus a lot of those image hosts such as photobucket and imageshack are blocked by a lot of workplaces (mine) so people viewing the site from work wont' be able to see your maps.