Establishing communication
The first question, that came to my mind, was: why should the Thargoids
do something complicated in this way to tell/show us something, if they
already were able to talk to us and give as instructions/missions? At
least this happened in the older Elite series. And I assume, that the
Thargoids haven't forgotten anything about there biggest enemies ...
Then look at the images: they are a mirror of our visual representation
during the contact - the most simple way to exchange a message created
by an intelligent brain: not the same, but a reduced image created by
connected dots. So we shall recognise, that there is something, that's
able to distance itself from the exact visual it sees. Abstraction is
an essential part of intelligence.
Secondly the image shall make sense out of a combination of ordinal
information (letters) converted into a 26x26 matrix. We shall find
ourselves (or our visual representation) in the transfered image.
This can either be a test of our intelligence or the base for further
communication. I guess, the next step will be either a bigger matrix
or different images.
Morse and the alphabet
If you look at the drawings, the order of the alphabet is essential
to create the sketch - every exchange of a letter would change the
image beyond recognition. On the other hand, the letters come to us
through morse code.
But if you look at the morse code without knowing the alphabet, you
would never come to an order like a,b,c,d,e ... Morse itself is based
on the frequency of (english!) letters. So if you just analyze a stream
of morse data and count the commonness of the signals, you would end
with a sequence, that would look like e,t,a,n,m, ... Now what would you
do, to create that 26x26 matrix, just based on a stream of morse
signals? I wouldn't even use morse but a simple ternary system and
order it in a way like . - .. -. -- ... -.. .-. --. --- and so on.
So "they" must know both of it: the morse code _and_ the alphabet. And
because they connect the sound with an only for humans reasonable
sequence, they must want to communicate with
us, not with themselves,
or the Thargoids.
Our first signs of live
Why morse code? Why sound and not blinking lights? The first radio
broadcasts, that left earth and contained intelligent signals were
morse signals. They were regularly used from 1900 onwards. Because they
move with speed of light, they should be perceptible in a distance of
1400 Ly at the year 3300. So I guess, that "they" first stumbled upon
our radio broadcasted morse signals. Now they either just want to show us, how they
became aware of us, or they think, that morse is still an important way for us
to communicate.
But that is not enough to convert morse into alphabetical letters. They
must have followed the signals to their origins and must have found
something like a morse/alphabet rosetta stone. Unfortunately I didn't
find evidence, that something like this is on the pioneer or voyager
plaques. Further research is needed.