levo - 10:55 pm on Feb 1, 2013 (gmt 0)
I think there are three things you can do.
1. Blocking Googlebot and/or Googlebot-Images to your images.
- I believe (correct me if I'm wrong) images do effect ranking of page. I wouldn't recommend just blocking access to images via robots.txt or .htaccess
2. Hotlink protection
- Signed-in users and others using the https version doesn't send any referer. It won't work for those users. Also you're out of luck if you're using a CDN.
3. noindex images
- If you want your images out of Google's index, I recommend using X-Robots-Tag. It shouldn't effect ranking or Google Instant Preview.
<Files ~ "\.(png|jpe?g|gif)$">
Header set X-Robots-Tag "noindex"
more info on x-robots-tag: https://developers.google.com/webmasters/control-crawl-index/docs/robots_meta_tag