So I am planning on charging people for using my site's content. The way they could use it, is I would give them an iframe, which they could embed into their site.
Now what if someone embeds this iframe into their own site without my permission? a) How could I find out which sites are using an iframe of my site? b) Is there a way to programmatically prohibit such behavior, for example show an error page or just an empty site, if the iframe is embedded into a page, which was not previously verified by me?