Loading images on demand / lazyloading

After seeing google images nifty on demand loading I’ve been very interested in it

I’m wanting a wide strip of images to lazyload if the user makes their browser wider (click drag, maximise, whatever)

I’ve been looking around but can’t find much

The main one I keep seeing has a warning on the front page saying it’s no longer useable:

Other comments I’ve read about various lazyloading say that they don’t actually load ‘on demand’, but load all the images when you first load, and just fade them in when you scroll to make the image visible, which makes it kinda pointless

Is there a solution out there that works properly?

How does google do it? I tried to look in the code but was a bit lost