[dagw]

This means it's very, very difficult to come up with another document that returns the same string when run through this same function.

This isn't entirely true for some hashes (like MD5). However coming up with another Haiku, in English, that makes sense and has the same hash, is probably close to impossible.

So this probably wouldn't work that well as a service to see who first generated a random string, but works very well if we know something about the structure of the string in question (like that it is in a known human language and makes sense)