In a Google hangout, one SEO professional asked about a particular implementation they were working on to improve a CLS metric, involving potential use of image structured data.
They asked: if an empty SVG is used as a placeholder in the SRC attribute, and then the SVG is replaced with the original image once it loads, is doing this the same to Google?
This is something recommended on Web.dev. However, instead of using the data source set, they use their data SRC. They also switch an image with an image within the SRC.
They wanted to ensure that this type of setup is acceptable for Google, in terms of indexing images.
John explained that it sounds fine the way the SEO professional described it. For Core Web Vitals, he also mentioned that it’s something you can test to determine whether it works or not.
For indexing, it’s important that Google has information about the images on those pages. In John Mueller’s example, he said structured data is important. But, in our experience at iloveseo, this could also mean image alt text or image titles.
John’s advice is to always make sure that there is structured data for those images. In that case, Google is absolutely able to pick up that structured data in order to understand it.
What’s truly important is what’s physically rendered on the page and viewable by Google themselves.
This happens at approximately the 2:07 mark in the video: