Here's the translation of Rebel.jpg's text:

You must join or die
Join the T-Race's federation
and kill the gigerdians.
(Offer valid only if you are member of one of the first one races)
We recommend you to look at file rebel.jpg in this directory.
We wait to conquer the gigerdian empire after we have liberated our people.

Encounter deadly threaths.
See dangerous aliens
and kill the galaxy.
No dangerous job bonus included.

Help the T-race to
rule the universe.

We say that we
are allies with
these inferior
races but soon
we will conquer them all.