That's a really interesting technique! I'm trying to think of what else could be done with the encryption / description, but tracking is a really effective use

That's a really interesting technique! I'm trying to think of what else could be done with the encryption / description, but tracking is a really effective use case. Could probably encode some other secret messages in there, make a blog post about cheese include a hash to a pastebin. It also reminds me of the importance of having strong validation around things like usernames, because if I had a username that looked official but contained an invisible character... Related: ICANN explicitly forbids domain names from including zero-width space.