I found some lazy loading script on google but couldn't find the way they prevent images from loading.
Thanks in advance.
Edit 1: The script you referenced merely checks to see how far you've scrolled the page down and then determines which images are visible (or almost visible) by checking their top -- see the $.belowthefold and $.rightoffold extensions.
The example works great when the images are all the same size, because their containers can also be the same size and you won't get any odd page resizing behavior when you lazy load them. If you images' heights and widths vary, you may get some odd results.