Resize Photos in Web Directory to Specs Automatically

We are looking for someone to install a program, or write a script, that will automatically resize every .jpeg photograph in a given web directory to our specifications. File names must be kept the same. Image files are uploaded to a particular directory automatically, of all different sizes. We want to be able to cap file size at, for example, 640x480. All this needs to happen automatically, every time new files are added to the directory. The goal is to ensure that every image is no more than ~30kb. I hear something similar is possible through the program ImageMagick. Our web hosting in through Host Gator. Overview: -resize .jpeg images on web server automatically to dimensions/file size specs -image name stays the same -happens completely automatically, every time a new image is added to the directory -web hosting is on Host Gator Thank you very much.