Need gray scale image dithered to black & White, Can show in GIMP the process that works.

I have a number of images I need put into black and white imaging. I can show you the steps in GIMP to get the images like I want, you just need to follow the steps on about 100 images (actually I think the count is 103) images to convert. They are all very small. The images (about 15 or 30 per page) are in powerpoint.