Although called Slow Scan TV, it’s not TV in the normal sense of the term.
SSTV is simply the sending and reception of “still” images or photographs etc.
Originally photographs etc were converted to audio frequency signals for transmission, of course, with the PC now being common and powerful enough to manipulate images the majority of images are now computer
As with other digimodes SSTV has various formats, the most common being Martin and Scottie.
The images are transmitted line by line over a period of around minute which goes to explain why a single image rather than motion pictures are sent.
Of course, technology and modes are advancing all the time with this analogue style of SSTV slowly making way for digital versions.