I vaguely remember this existing from the early 2000s. That said, I recently decided to look into the fax machine protocol because there's a surprisingly large

I vaguely remember this existing from the early 2000s. That said, I recently decided to look into the fax machine protocol because there's a surprisingly large amount of legacy use in Japan and it seems like there's a good market to replace it with an app. You wouldn't even need to use VoIP because the hardware literally has a phone connection. In my research I found an early stack overflow thread from the 2010s where I learned that the thing protecting the fax industry is a ton of obtuse standards that require payment to access. What little documentation I did find came from an obscure public information server on the ITU website. Apparently there are 3 generations of protocol. The first generation worked like scan lines in a television except the carrier frequency was audible and it was very slow scan (a few min per frame/page). The later revisions were digital in nature and from what I understood they compress the scan into continuous regions of white and dark. The exact compression scheme was very obtuse so that's where I gave up. I also could not figure out the handshake part of the protocol which happens when the call first connects. Good luck to anyone who wants to pick up where I left off.