I've downloaded this mod on SA2.0.77 (linux) and tried to make a few screenshots with it.

There is no sign of these images anywhere.
Looking into the code doesn't reveal much when it comes to the saved location: the hint that is given is relative and there is no indication of what that path is relative to.

Looking at the original mod that this was forked from, there's a location mentioned in the readme that the screenshots should be saved in ~/.factorio, and that should be the base path.

I do not have that directory, as the game is installed somewhere else.
Even if I make that directory myself and then a screenshot is taken, the files are not created.

Is it possible to:
1) make the save location configurable, so that you can specify exactly where to save things and
2) make that location visible in the hint, so that it is clear exactly where the new files are stored?

Alternatively, if that cannot be done, can the logic be updated to create the path if it does not exist? Right now the screenshots are basically saved in /dev/null.

Thanks!

I'm also running the native linux version.
The save path is in ~/.factorio/script-output/screenshots/<map-seed>/
Read more here Factorio Wiki

As it's usually in your home folder, there should be no issues with write permissions.
I just tested it and the folder structure and files were created.

Regarding 1.
Unfortunately as far as I know script-output is the only folder any mod can output/save files to.

Regarding 2
I could extend the chat text to show a bit more of the location but script-output is the only path where mods can do anything relating independent file manipulation anyway as it's intentionally locked down for, I guess security?

Okay, that does clear things up a bit for me.

I was searching for the created png files in various directories but I thought the file name would be exactly what I typed. Looking at your directions I managed to find the correct screenshot directory which was indeed in the <factorio base dir> which in my case is in /data/games/Factorio/game/.

So what happened is that I have the Gog.com version of the game which puts factorio and its expansion in different directories.
So the path didn't match what the readmes say.
Either way, that directory does contain the script-output dir that you refer to. The images were indeed created there, though not with the names I expected.

So all in all it was just a case of the paths not matching what was specified probably due to the installer that I used. That might be good to add in the readme for others.

With that, the options I mentioned aren't really necessary anymore. So no need to worry about it. I was being dumb.