Google Supports X-Robots Noindex to Block Images for Googlebot
Google respects x-robots noindex in image response headers.
Google Chooses a Higher Resolution Image Where Multiple Versions Exist
If you have both high and low resolution versions of images, Google will prefer the higher resolution version.
Image Sitemaps Help Google Understand Which Images You Want to Be Indexed
Google can find images to index in the source code, but Sitemaps can help them to confirm which images you want to be indexed.
Unique Images are More Likely to Generate a Link to Your Pages in Google Image search
Google image search will de-deuplicate images used on multiple websites and only link to a single page with the image, so a unique photo can be shown separately.
Alt Text Helps Google Understand Pages Beyond Image Search
Text in the alt attribute of images is seen as text on the page and can help Google better understand the page a little bit better beyond image search. However, the text in the alt attribute will likely be somewhere on the page anyway.
Image Aspect Ratio Important For Some Types of Structured Data
Image aspect ratio can be important for some types of structured data and rich results like recipes. John recommends following Google’s suggested image aspect ratio and minimal size.
Check Alt Text is Present on Mobile Version of Images
John recommends checking that the alt text is present for the mobile version of images for mobile-first indexing. This is something Google has seen missing from sites that serve different content on mobile.
Avoid Using Lazy-loading For Crucial Images & Content
If you have images and content that are essential to the website, then avoid using lazy-loading for these elements as Googlebot isn’t always able to process them.
Image URLs Can be Flagged as Soft 404s in GSC
The GSC Index Coverage report may flag image URLs as soft 404s if they have a non-standard image URL. This is because they are seen as a 200 page without any HTML.