OR you can do what I do an have small images as the default image located in /images approx 15-20k each
Then medium images located in /images/medium approx 30k each then large images in the images/large approx 200k

Image size / quality is totally what you want it.

It takes about 30 mins for me to batch create 3 different sizes of 7,500 images and upload to the site.

Either way one or the other is the best option over using just 1 image and loading that size image for everything so either use the zen image folder sizes or IH.