Google has said before that they can't see lazy loaded content on mobile but said it is a tricky situation. That was back in 2015, about three years ago. Now, Google is going to work up some advice and help documents around how to make lazy loading content and images more discoverable by GoogleBot.
Why is this important? Well, for site speed. One of the main reasons a site can load slowly is images and lazy loading those images, loading the images as the user scrolls towards it, is a great way to speed things up. I do it at RustyBrick.com and it really helps with the vanity PageSpeed score. :)
Now John is saying there are ways to get that content indexed and Google will work on clarifying how to do so.
John Mueller said on Twitter this morning "there are various ways to lazy-load images, it's certainly worth thinking about how the markup could work for image search indexing (some work fine, others don't)." "We're looking into making some clearer recommendations too," he added.
There are various ways to lazy-load images, it's certainly worth thinking about how the markup could work for image search indexing (some work fine, others don't). We're looking into making some clearer recommendations too.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) February 28, 2018
I cannot wait to see what Google puts together around this, as I've been expecting it for some time and I am a bit surprised it is not out yet.
Forum discussion at Twitter.