In order to allow a site owner to control settings about tagging on their site/images, we first need to establish who they are. To do this we decided to follow the same model used by Google Apps and a number of other services.
While taggr can be used with any website just by inserting the relevant HTML into the page, to have full control over moderation of users/tags, control of which images are taggable, etc. the webmaster will need to link their domain to their taggr account.
To do this they would add a <meta> tag to the website. We chose this rather than the other options used by Google (TX Record or uploading a file with specific content) because of the large amounts of blogs which are stored in subdirectories rather than subdomains. Most of the 150+ million blog owners would be unable to establish ownership of their website if we required a file upload or TX record.
Each subdomain can be assigned to a different owner to its parent, otherwise it defaults to inheriting the ownership from the parent.