I browsed 4chan /x/ earlier today, so here's where they are...
The obvious one relates to the fact that founding members of the Federal Reserve were on the Titanic, and it was intentionally sunk to (something incoherent about economics). The submarine was sunk for similar reasons.
The Titanic didn't sink, but it was some other vessel, and They had to sink the submarine so the truth wouldn't get out.
There are deep ocean aliens, and the sub had to sink to conceal that fact.
Those are the ones I could remember. In any case, it's always the Jews and the CIA.
We routinely take photos in other frequency ranges. It's easy enough to find infrared photographs, made easier since not only is there film that exposes IR, but digital cameras are naturally sensitive to it so you just need to change out some filters. But you know, astrophotography often uses different frequency ranges, since a lot of stellar phenomena emit different kinds of radiation.
The bigger question is, would an alien without eyes at all be aware of electromagnetic radiation? And conversely, what phenomena are there that would be obvious to aliens but we just don't know about, because out sensory organs don't predispose us to being aware of them?