Originally Posted by johnnyloadproductions

Your best bet then would be to write a PHP script that you run on a local machine (your computer) and:

-resize a picture to a given size
-check the size of the image
-if the image size isn't correct, auto tweak the parameters for resize
-if the image fits a given tolerance (within 50KB of 6MB), move to the next original image to resize.

If you download and install WAMP, this is something you can do.