The ‘Alien photo took down 4chan’ saga has turned out to probably be all one big joke.
There have been a load of images re-posted and shared around claiming to be the original photo but none have been confirmed as definitely being the original. Most you can tell have been knocked up on Photoshop.
However it seems that it was all a big hoax after all.
It was apparently orchestrated by a Discord group. They were taking advantage of a maintenance situation. They found a bug on the site where they posted a thread and it got taken down immediately. They decided to take advantage of the bug and posted a mocked up photograph of a X-Files alien against a desert background.
Again the post immediately disappeared and when the site came back online they started posting that they had seen an alien pic just before it was taken down. Then it seems to have all kicked off from there.