Google’s John Mueller reminded us that when it comes to your CSS background images, Google won’t be indexing or ranking those images in image search. John Mueller said on Twitter “last I checked, we don’t use CSS background images for image search.”
John said this also back in January 2018 when he said Google Image search does not index and rank images from CSS background code.
The question wasn’t specific to background images but it was around if Google sees alt text of those images and the answer would likely be no.
Last I checked, we don’t use CSS background images for image search, so the point might not be that relevant (also, what would a background image rank for?). A simple way to check for aria labels indexing is to search for the text in them: https://t.co/w5dOfsjg0a (=not indexed)
— 🍌 John 🍌 (@JohnMu) April 12, 2021
Forum discussion at Twitter.