What's the privacy benefit over storing a tracking cookie with expiry of a day? If at all, random cookie seems better for privacy as in your case if someone really wants it, they can recover the IP if the user agent is not rare by searching for all IP(4 billion IPv4), User-Agent(100 for popular browsers), the date(1 day as date is stored separately), and a salt(known to server), easily within reach of anyone.

It doesn't use cookies. Fingerprints are calculated on each page hit.

The salt must be treated like a password to make sure it's not that easy to brute force it and no one should get access to your database of course ;) It's not the strongest anonymization, but good enough considering that the hits will be deleted once a day by batch processing.

Seems like a good method and actually more accurate than they do... seems like they just do a hash of IP.

Hmm I think I've read something about it elsewhere and they also use more parameters than just the IP. Not sure.