It sounds like you have a specific, non-western culture in mind which finds it very easy to talk about about sex.
Which is it?
> Before starting the blackmail, KGB invited Sukarno in a small private movie theatre and showed him the pornographic video, in which he was playing the main part. KGB agents were expecting him to get really frightened, that he would agree to cooperate with them at once, but everything happened vice versa: Sukarno fondly decided that it was a gift from the Soviet government, so he asked for more copies to take them back to Indonesia and show them in movie theatres. Sukarno said to flabbergasted agents that the people of Indonesia would be very proud of him, if they could see him doing the nasty with Russian girls.
More details here (along with the KBG story): https://medium.com/war-is-boring/the-cia-and-kgb-tried-to-bl...
Even though asian countries view sex as just another thing and not so much sex positive.
The referenced article in this thread mentions some of the history of the Lena image, but Wired did a good job finding the actual woman in question and talking about some of the social history. [1]
I was never on the Well, Fidonet, CompuServe, AOL, Prodigy or any other BBS systems, but from this article [2] you can see that low-res text-based block character "images" were possible. The minute you can make something display an image, someone is going to figure out how to put porn on it.
Apparently there was MacPlaymate, a 1-bit image depth interactive program (distributed on 3.5" floppies) from 1986. NSFW [3]
Usenet was definitely part of the early mass sharing of porn online, but as far as I can tell image binaries date (e.g. alt.sex.pictures.erotica.* or alt.sex.binaries.*) more to early 1990s, not 80s. Downloading low-res images over a 14.4 modem in multiple UUencoded text messages based only on a title (or perhaps a frequent, trusted poster) and re-constructing them into a GIF or JPG was very very slow, but where there's a will there's a way - or so I'm told...
[0] https://www.nytimes.com/1994/01/09/arts/porn-the-low-slung-e...
[1] https://www.wired.com/story/finding-lena-the-patron-saint-of...
[2] https://spectrum.ieee.org/social-medias-dialup-ancestor-the-...