ISS Slow Scan Television (SSTV)

Slow Scan television (SSTV) is a picture transmission method used mainly by radioamateurs, to transmit and receive static pictures via radio.
SSTV images are periodically transmitted from the International Space Station and other ARISS supported satellites.

To find announcements about transmissions, follow dedicated official ARISS blog:
Periodically ARISS dedicates special awards for SSTV events, here you’ll find any information:

After receiving,you can submit your decoded images and receprion reports in SSTV gallery:

For beginners, but not only, here is an AMSAT page very helpful:
Here you can find An SSTV decoder setup for Raspbian