square images without cropping?

hi, this may be already answered but I can’t find it on forums.

so, can anyone point me to a way of making images square without cropping (via adding white space and centering). It would be great if there’s a way to do it upon uploading but I’m not that into fantasies.
also this is supposed to be in bulk (1000+ images).

what i suppose it should do: take image, find biggest of width\height.
add to image lowest param the difference of params
and equally distribute additional dimension.
e.g. 800×600 image -> 800×800 image with 100 to up and 100 to bottom of image.

thanks for any and all answers.