Need to unload thumb that are not visible in G4?

I’m triyng to unload images that are not visible in G4.
This is to speedup the frontpage loading if you have a lot of aticles and/or new articles.
The loading time is worst if the article comme from external RSS (obviously as all images have to be loaded from external UR
I try some of the plugin in the JED but without to much success.

LAZY LOADER
http://extensions.joomla.org/extensions/site-management/site-performance/12273

LAZY LOADING IMAGES
http://extensions.joomla.org/extensions/site-management/site-performance/13380


They didn’t work. That will be a big speed improvment to integrate a kind of “Lazy Loading” and/or the ability to make rss external image internal.

It will help a lot in my case.

What can I do to improve the loading time...
Thanks