I saw a program some years ago, which was able to make a 3d
image/object from 3 or more 2d images. The way it worked was that you
would see all the different images, and then start by placing a point
on one image, and correcting it to the correct location on the other
images. And then combine these points to surfaces, and finally it
would make a 3d object out of it. It's actually very simple.

But of cause now that I need it, I can't find it. So, my question is,
do you know any programs that can do what I just described? Preferably
for GNU/Linux (as this is my primary operating system,) and even
better Open Source?

Another plus factor is if the program is able to export the objects to
Blender, or at least export it in some standart way.

The term for this is "photogrammetry" and the industry software that
is widely known is "Realviz" Imagemodeler from www.realviz.com though
you should be able to find numerous other programs that do this:
Photomodeler, Geomatica, Digicad, etc. I pulled up a half million
entries.