1970 article about using an oscilloscope to view SSTV pictures. As noted in the article the scope needs to have a few modifications performed. This biggest one being changing the CRT to a P7-phosphor version. Getting those for a modern scope is highly unlikely, unfortunately.
If you have a digital still camera with a 'B' or 'T' shutter setting may make this feasible without changing the CRT, though rather awkward.
The circuit these days could be somewhat simplified with the use of ICs.
Steve A.