Make A Lazy Loader That Loads In Images When User Scrolled To?

how to do a custom lazy load ???You know for instance... lets say I got 500,000 images to load on a page... it's inside a dive... well I want to load the images when it's needed.So not all 500,000 images will load all at once. I want like 10 to load at a time.. this will make the div scrollable.so when the user scrolls down to the 8th image it will load 10 more images and so on.

how to make their own function like this?how do you detect if the user scrolled to the 8th image? I am pretty sure I can use a function.... that will send variables to a php script that will use the mysql limit. The javascript would send a value which is where to start loading from the 10th image in the database.. meaning start grabbing the images from the 11th image onward for a max of 10 total images to display.