Web Site Pictures Help

I am bulding a web store and need to upload pictures to it. The problem is I need to upload 3 images for each product and for me it is easy, but also very time consuming to resize and resave a jpg to each size. I was thinking maybe there is a way to program a script to automate this process. The original image is max 400 x 400 and would be a jpg format. Then I need a max 200 x 200 medium size image, and finally a max 100 x 100 thumbnail size image. I am probably looking to do this to 60 to 100 products. Let me know if you have any questions.