Slow Scan TV (SSTV) is a transmission method for sending images via the airwaves. These image types could be GIF, JPG, BMP or similiar depending on the computer software used for the SSTV transmissions.
It works similiar to Facsimile transmissions. Each colour has it's own frequency in SSTV mode and the software simply codes the colour into an audible frequency tone that can be interfaced into the microphone system of the radio. The receiving end software simply decodes the frequency tone back into the colur.
In fact, an SSTV signal can be recorded onto an audiotape and then played back and decoded. Any number of people can simulatenously decode a single SSTV transmission, just like 1000's of people can listen to the same radio station at the same time or watch the same television channel.
SSTV is a relatively fast method of transmission, each transmission burst of SSTV lasts about 30 seconds irrespective of file size.
Information contributed by John - VK3TVZ
There is more recently a digital SSTV mode known as EasyPal that is also in use on the Amateur Radio bands. You can see a YouTube video by Erik VK4AES about this.
