graphics - How to do this sprite motion blur?

Some of you may know fraxy...

Basically, I was watching this video: http://www.youtube.com/watch?v=uL7zWdDCtOE And there are some times where some sprites spin really fast (4:00 mark for example), and I cannot figure how the motion blur effect was done.

I looked in the game folder, and found the sprite, it certainly does not has the blur added to it (in fact, it is even a .bmp! Not a PNG or anything that supporta alpha natively), and the engine IF using OpenGL, may not be clear (the resolution is fairly low too), also nothing else is getting blurred (so the effect is localized to some sprites... if you pay attention there are other moving objects that get blurry too).

So, how they do this glowing blur?

EDIT: On the video I am talking about the two things "spinning" in the left and right edge of the screen, they are shooting, and the sprite of their bullets are the same as their own sprite, but if you pay attention as they spin their sprites leave a trail, actually if you put the video some seconds before, you will see with the screen more empty, and the effect can be seen clearly.

EDIT2: I don't think Fraxy use shaders, and I am sure it does not use OpenGL either (since it run on computers that don't run OpenGL games). I know it is easy to do with shaders, with per-pixel calculations, I am asking how to do WITHOUT them.