I’ve enjoyed looking at these photos of Pluto from 3 billion miles away. Just for fun last night, I found some information on the old Lunar Orbiter probes that mapped the moon from 1966 to 1967 in preparation of the Apollo landings. You should take a look at the technology they had to use to transmit the photos of the lunar surface. By our standards, primitive. The probe took film photos, processed and developed the images, and then had to convert them into digital images to transmit to earth. Primitive, but also ingenious.
The digitizing of photos for sending over wire — basically, fax — has been around since at least WWII. The famous Iwo Jima flag-raising shot got to the US for distribution via fax.
Here’s why it takes so long to beam data back from Pluto
http://www.businessinsider.com/why-it-takes-so-long-for-new-horizons-to-send-images-2015-7
More in depth:
Talking to Pluto is hard! Why it takes so long to get data back from New Horizons
http://www.planetary.org/blogs/emily-lakdawalla/2015/01300800-talking-to-pluto-is-hard.html