I found this while nosing around the high-frequency radio bands. Shipping interests and small craft on the open ocean don’t always have access to the internet. Charts like this are transmitted line-by-line over shortwave using radio fax. Each of these charts took about 10 minutes to receive from a transmitter in Boston. It is old tech and it is excruciatingly slow, but for some mariners, it is still valuable.
Between 1930 and 1970, fax technology was the main way photos were sent from distant places. It was a staple of newspapers and magazines, and those old enough may remember photo captions like “Associated Press Wirephoto.” If the photo came from overseas, it was likely it came at least part of the way via shortwave. The image of the raising of the flag on Iwo Jima is a famous example.
Interest in high-frequency radio has grown again as government, business and the military are becoming more aware of the severe vulnerabilities of internet infrastructure. Satellite and internet communications will be supported by good old radio.