What exactly are you trying to accomplish in the animation, by changing the body part for every frame?  Is this still related to the breathing example you posted in another thread?

And I'm not quite exactly sure what you mean by this:

1. Animate the human model (frames are set automatically) - this is pretty straightforward. 

2. The human model of each frame is separated and recognized as a still image. --- Why are you converting the human model to a still image?

3. Call the two images one by one and edit them with a script.

4. Export all edited images as obj file --- Again, not sure what you mean here. You want to convert an image to an OBJ file? That isn't possible AFAIK. Definitely not possible in Poser.