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Extensions > lazy_load
Lazy Load 2.0
Load images only if the browser displays them
The extension "lazy_load" loads the images only if the browser is going to display them. If images are out of the range, they are not loadet. So your site is loading faster and the user save some traffic. Both sites win :) The options are in the root page.
There are no bugs reportet yet. If you found a bug, please report them in the Forum or in the Bug Tracker at Contao Forge.