A pure javascript way to lazy load images without a server can be run by just dropping example html file into browser.
Works by getting the image tags which have a data-src tag instead of a src tag on them, then detecting the boundaries hit the scroll position + window.innerHeight and setting src on the image causing the iamges to be loaded.
This requires javascript if javaascript is disabled then the lazyloading images won't load.
example:
Horse: https://www.freeimages.com/photo/horse-1393073
Butterfly: https://www.freeimages.com/photo/butterfly-1392408
Goat: https://www.freeimages.com/photo/my-beloved-mountains-2-1375135
Rope Knot: https://www.freeimages.com/photo/hunter-s-bend-1316926