What file(s) would I need to edit to add the meta tags?
themes/yourtheme/template.html
1. Use .htaccess and make user accounts for your invited guests.
2. Use .htaccess and set a new default index (so no one will find it by chance)
3. Disable registration, make the gallery un-view-able for guests and give the accounts to your guests
That would be a brute-force method that will shy away legitimate users who are not so computer-savy. The first option (keeping the major search engine spiders from indexing your site in the first place) by editing the robots.txt file is the best solution. No need to edit the meta tags if you disallow indexing in robots.txt, as the spiders of "good" search engines will respect robots.txt and stop indexing at once without even looking at your pages or having to read the meta tags. The "bad" spiders will (like email harvesters) disrespect both robots.txt as well as the meta tags, but they won't lead to your site getting indexed on publicly available search engines anyway, so there is little need for concern. The brute-force method with an alternative .htaccess-based authentification scheme will (as suggested) scare legitimate users away and won't teach your newbie-users how to get access (by contacting you) - they will instead just leave for good. If you're very concerned about privacy, your strategy should be three-fold:
- Set up robots.txt as suggested
- Add the nofollow and noindex meta-tags to themes/yourtheme/template.html
- Set up your gallery to make registration mandatory (in coppermine's config, set "Allow unlogged users (guest or anonymous) access" to "no") and enable registration approval (again: coppermine's config - set "Admin activation of registrations" to "yes"). Search engine spiders will not try to register, and you will be able to tell illegitimate and legitimate users apart and only aknowledge valid user registrations.
When disallowing anonymous access, both search engines as well as illegitimate visitors won't see actual private content, but your unexperienced legitimate visitors will at least have a nice user interface that will tell them that they need to register.