In case anyone hasn't seen the picture referred to, it's this one
I have little to no understanding of how early Soviet information/propaganda worked, who issued these pictures, through what medium and who the intended audience was (and if they bought it). But it always struck me as weird that a government ruling millions of people would feel compelled to change one particular picture. I get that dictatorships use images and why they do it, but I'm confused by how feasible/useful going after individual ones already in circulation would be.
From my entirely uninformed point of view, it would be easier to say "Here's comrade Stalin next to our new awesome tractors!" than arguing "No, there was no one next to the General Secretary on that day, just some weird squiggly lines".
I would love if someone could give me the necessary context to understand Soviet era picture manipulation and, most likely, clear up the misconceptions in my question.
Hopefully someone can provide more information, but I might be of some assistance in the meantime with some background from this answer and this answer I wrote for the Short Answers thread.
Generally speaking the photographs in question were official photographs, so things like official portraits or photos approved for use in publications (like the Soviet Encyclopedia). Most of these sorts of changes were in fact done by publishers (it was apparently never an official practice organized by its own bureaucracy, but "heavily suggested", if you will). Probably the two most (in)famous airbrushed photos are the photo of Stalin with secret police chief Yezhov, and a photo of Stalin, Nikolai Antipov, Sergei Kirov, and Nikolai Shvernik - this one being special because eventually everyone except Stalin was airbrushed out and it was retouched to be a Stalin portrait.
These are probably the most famous and sinister examples for the blatant removal of purged political figures, but they're not necessarily the most ubiquitous retouched photos. A famous photo of Stalin with Lenin at Gorki in 1922 was very widely publicized and used as the basis for public monuments, and was extremely heavily touched up - Stalin was made taller and had perceived physical imperfections removed, and it apparently is actually two separate photos stitched together. A bonus famous example (OK, this does involve removing political enemies) is of Lenin addressing soldiers outside the Bolshoi Theater on May 5, 1920. Honestly there's a good chance you might think of this photo when you think "Lenin", which probably puts it into a Bolshevik version of a meme. Trotsky and Kamenev (two enemies of Stalin whom he later had killed) have been removed from the photo. They wouldn't necessarily have been prominent but this was an incredibly widespread photo, again used in publications, history books, and as the basis for other types of pictorial art, and so removing those two from the official version was important.
As for why this was done - these were mostly done in the context of the Communist Party purges of the late 1930s, when Stalin was going after perceived enemies and their associates within the Party itself. The Communist Party of course had its cult of personality for Stalin, but smaller "cults" for other party figures, so when Stalin denounced some of these senior members as traitors and foreign spies/terrorists, it wasn't just denouncing nameless, faceless functionaries - these were big name people who were well known in their own right. Having official photos of them floating around was awkward, to say the least - it's a bit like that photo from circa 2000 of the Clintons and Trump schmoozing at a party could be seen as awkward from 2016 on. And again while it wasn't an officially-stated policy to airbrush such people out of photos, there was clearly a motivation to do it lest the publishers themselves get accused of making some kind of anti-Stalin political statement.
More on this subject can be found in David King's The Commissar Vanishes: The Falsification of Photographs and Art in Stalin's Russia.
/u/commiespaceinvader has previously written about the use of photos as primary sources with additional input from /u/hillsonghoods and /u/restricteddata
