SSTV is a form of encoding allowing You to transmit pictures over virtually any transmission medium that allow uncompressed human speech – starting from phone ending on SSB radios. It’s similar to “fax” that was used over landline.
For testing i decided to record couple of SSTV sample audio files using different encoding to compare quality.
The slower (longer time) works better on noisy frequency like SSB.
Quicker one working perfect over AM/ FM.
Here are files for testing, You can decode them from “speaker” using Android smartphone and application called “Robot32” <- don’t let name mislead You, it decode all modes used here!