Community manager at Trovebox here. To go along with the other Trovebox-related reply, we're planning to start work on an iPhoto plugin for Trovebox soon because we've gotten so many requests for it.

If you're specifically looking for Flickr, a little searching shows me this page, which mentions an (unofficial) iPhoto plugin: http://www.flickr.com/tools/

Something like Trovebox[0] might be a solution to your needs. You can use it as the web frontend to photos stored on dropbox/s3/box/etc

[0] https://trovebox.com/

Uploading from iPhoto's share option, the default option is for photos to only be visible to you.