Batch resize by adding white background to make it 1:1

HI,

I tried to search this topic but I couldn't find the one I'm looking for.

So I have thousand of pictures with different sizes

1024x683

3456x5184

550x550    (aspect ratio 1:1)

So the sizes are all over the place.

I would like to make all of the pictures to aspect 1:1 by adding white background.

By adjusting each picture to it's biggest height OR width and NOT cropping or changing the size of the actual picture.

So basically like this:

1024x683        ------>>  1024x1024  (adjusted to the height)

3456x5184      ------>>  5184x5184  (adjusted to the width)

550x550  ------>>  Not changed  (aspect ratio 1:1)

And the pictures should be in center of the added white background.

So basically just adding white backgrounds to the picture.

And doing that in Batch for thousand of pictures.

Could someone please teach me how I would do this?

Thank you.

Robert   

EDIT: I forgot to mention that I use CS6