There is a similar issue being treated in StackOverflow,

https://stackoverflow.com/questions/22685274/divide-an-image-into-5x5-blocks-in-python-and-compute-histogram-for-each-block

In there they use a histogram on each subframe, you can apply your own process. Afterwards, reversing the process you can create the new image.

Hope it's useful!

use normal data slicing or normal row-column operation in python. Or you can do by numpy or panda...

Here is a quick solution that can generate from 4x4 to n*m blocks. Add a check while loading image file to make sure that your image is properly padded.

https://github.com/QuantumNovice/ImageProcessing/blob/master/image_chunkify.py