Parallel Python or the multiprocessing module require the objects which need to be passed around to other processes to be picklable, and the image object from PIL is not.
I recommend removing the call to image.putpixel from the function to be parallelized, returnin a simple list of RGB points or a numpy array which are picklable. then, after the calculations are done you can assemble the image.
Also, in order to get more specific advice, you should post the parallel version of the code as well.