So, the greenshirts are a GoI. It’s never explicitly stated whether they’re a precursor to the Foundation, the Foundation from an alternate universe, or just an unrelated faction. However, there is a small hint that implies that they’re a Foundation precursor:
only thirteen of us left
I just threw that in because it’s my headcanon. Anyhow, the GoI began by just searching for anomalies, but soon decides to use the SCPs to weaponize themselves to fight the more dangerous ones (Keter). The bloke writing the note is vehemently against this, but he gets overruled.
The culmination of this is the photograph. Since the GoI is tracking and snatching anomalies from the shadows (another nod to the GoI being a Foundation precursor), they need to make people forget. And how should they do this, but with an anomaly?
They task the science guy with creating something to help them forget. And lo and behold, the photo is created. Thing is, it becomes slightly too good, and starts erasing the memories of random people. So then they need the scientist to reverse its effects. The trouble with that is that he can't remember how he created the photo.
Suddenly, he realizes that, since it's a photograph, there must have been a negative of that photograph which would have the opposite effect. Sure enough, it exists, and it's indestructible.
However, the problem with the Negative is that it doesn't restore memories - it gives people random memories it had erased. Memories of anomalies, as experienced by people who didn't know what they were. Hence, the D-Class testing logs in the first addendum recalling random memories of anomalies.
This caused serious fractures within the GoI, and by the time they stopped using it there were only thirteen left. Through mysterious circumstances, twelve of the thirteen died, leaving only the scientist left with both photographs. The scientist writes this note, stares at it for a long, long time to increase the chances of it being remembered, then glances at the positive, and forgets everything.
Where does this leave us? The article is about the negative; it restores the wrong memories, but since it happened so long ago there were no memories to overwrite in the D-Class. This means that somewhere out there is a photograph able to completely erase anything from your memory. Who knows… maybe someone has it. Maybe someone is using it to remain completely invisible, from everyone including the Foundation.
Also, quick secret: read the first letter of every paragraph for a hidden warning by the author.
Modulum
CaptainGirth
Benjamin Stokes
Alfred Hitchcock
Icepick