Joomla Defer Images plugin (Lazy images).

This plugin makes your images loading when it is needed (LazyImages) or show all images after the whole page loaded (OnLoad).

First, it replaces images with small image as 'data:image' code.
Then, when you load page and scroll, it loads an images which on the actual screen or load all images after page loaded (OnLoad).

The plugin parameters:

Defer type - Select which images loading type you need (LazyImages by default);
- LazyImages - makes your images loading when it is needed, when you load page and scroll, it loads an images which on the actual screen;
- OnLoad - load all images after the whole page loaded with OnLoad event.

Images Load Delay - Delay for load deferred images on page load;

Read more http://feeds.joomla.org/~r/JoomlaExtensions/~3/w-g1oyhv-Ok/defer-images