Scramble a picture

[S_H]

Hi,

I'm looking for an automated way to scramble a batch of images. 

That is, to automate this process on a folder of images:
1. upload an image
2. slice the image into 9 equal pieces (the images are not in the same size)
3. completely shuffle the pieces order (such that upper left must not stay in upper left) without changing the image size
4. save

I found ways to do step 2, but because my images are not in the same size I don't know how to batch it. 
I Particularly struggle with step 3.

Thanks a lot for your help