Images Implemented Via Lazy Loading Can be Used Like Any Other Image on a Page
Images implemented via the lazy load script can be added to structured data and sitemaps without any issues, as long as they are embedded in a way that Googlebot is able to pick up.
Ensure Embedded Images Are Clearly Marked As Images
If images that are embedded on a site are not clearly marked as images, Google may not be able to see or index these e.g. using CSS to embed images. This is particularly common when the code is different for desktop and mobile versions of a website.
URL Inspection Tool Live Test Might Not Load Embedded Resources
Embedded resources might not be loaded using the live test URL Inspection tool if they take too long to load. This doesn’t mean that the embedded resources won’t be loaded for indexing, as Google has designed the tool to provide relatively fast insights.
Content in Iframes May be Indexed on the Embedding Page
Pages embedded within an iframe on another page may be indexed as content on the embedding page as it will be seen when the page is rendered. You can use X-Frame-Options to prevent browsers from embedding a page which Google will respect.
Add Tag in Header to Specify Don’t Want Content Embedded in iframe
You can add a tag to the header of your page which will let browsers know that you don’t want content to be embeddable as an iframe
Add Alt Text and Embed Images on Mobile Sites in Preparation for Mobile-First
Google’s Mobile-first team has noticed many sites don’t include alt text for images on mobile sites. John recommends checking that alt text exists for images when checking sites are ready for the switch to Mobile-first indexing as well as making sure images are embedded so they can still appear in Image search.
Google Establishes Original Content Sources
If multiple sites are using the same affiliate/product content, Google will try to establish the original source, and allow a few other version to rank. They will be treated as separate sites which can rank independently for different queries. The suggestion is that this is fine provided you include some unique content. Later he also suggests this for pages with embedded videos.
Make Video the Main Focus of a Page
If you have unique videos on your pages which you want to appear in search results, you should make sure the video is prominent, and the main focus of the page, or the video snippet might not be shown.
Disallowed CSS/JS Is a Problem If It Prevents Rendering
Disallowed CSS and JS is only an issue if it actually prevents Google from finding visible content, or rendering pages correctly. Other JS files don’t matter so much. There aren’t any penalties or anything like that.