Google Image Search usually doesn’t find images specified within a CSS background attribute
A question was asked in this session about whether a pure CSS background image would be picked up by Google Image Search. John relayed that, to his knowledge, this would not be picked up by Google Image Search. To help Google find these images, it’s best to make sure it’s linked within the page, if you care about the image appearing in Image Search. For Image Search, Google’s algorithm mostly looks at the image alt tag, the title tag, and the text around the image on a page.
Alt text associated with a linked image is treated the same as anchor text
A question was asked regarding an “a href” tag that contained anchor text and an image with alt text. Which one helps Google to better understand what the linked page is about? And does the order in which they occur within the tag matter? John replied that the order of these two elements within the tag would not matter. With just an image, it wouldn’t be as valuable as anchor text, but if alt text is associated with the image they would treat that the same as anchor text. It would be converted into text on the page and treated the same.
He did further clarify that this news shouldn’t mean that all visible text should be removed and alt text relied upon. But it should help to know that you’re not losing anything by including both. Other search engines may not see alt text and anchor text as equivalent and for accessibility and usability reasons it may make sense to have visible text there too.
It’s not possible to control which images appear in rich snippets
It seems that images are increasingly being used in the rich snippets shown in the SERPs, but there’s currently no way to tell Google which images are preferred for this purpose. The only option is to use the ‘noimageindex’ meta tag on images that you definitely don’t want to appear in snippets, but note that this particular tag will prevent those images from being indexed entirely.
Regularly changing image URLs can impact Image Search
A question was asked about whether query strings for cache validation at the end of image URLs would impact SEO. John replied that it wouldn’t affect SEO but explained that it’s not ideal to regularly change image URLs as images are recrawled and reprocessed less frequently than normal HTML pages.
Regularly changing the image URLs means that it would take Google longer to re-find them and put them in the image index. He specifically mentioned avoiding changing image URLs very frequently, such as adding a session ID or today’s date. In these instances it’s likely they would change more often than Google would reprocess the image URL and would not be indexed. Regular image URL changes should be avoided where possible, if Image Search is important for your website.
Images should also be redirected during a website migration
John answered a question about organic search fluctuations after a site migration. As well as checking the page differences before and after in regards to aspects like internal linking, content or structure, it’s also important to consider embedded content like images.
If you don’t redirect your old image URLs, Google needs to reprocess them again and will find them again as new because they don’t have the connection between the old and the new URL ones. He clarified that it can have a big effect if you have a lot of image search traffic. It makes sense to set up those redirects even if you’ve moved over a month or so ago.
It’s recommended to keep the same URL when converting image file formats
Converting image formats (for example from JPEG to WebP) has the potential to impact existing rankings. Where possible, it’s recommended to keep the same image URLs and just swap out the files. Otherwise, Google will need to discover and index those new URLs in the same way it would for text-based content.
It can be beneficial to have a separate image landing page if you care about image search
John mentioned that for Google Image Search, having a clean landing page where, if a user enters a URL, they land on a page that has the image front and center (perhaps with some additional information about that image included in text) can be really useful because it’s something that the Google systems can recognize as being a good image landing page.
For example, if yours is a portfolio website with 30 small thumbnails on it and the image from Image Search is hard to spot (or could have moved out of view), users may feel confused if they were sent there from the Image Search results page. Google Image Search works separately from normal web search and not all websites will care about it, so this may not be something that needs to be considered if you are only interested in web search.
Image sitemaps can be useful for sites that use lazy loading
When “lazy loading” images on a page in a way that doesn’t include defined image elements, it’s recommended to have back-up in the form of structured data or an image sitemap. That way, Google will know to associate those images with the page even before they’re loaded.
Img Alt Text is Used for Both Web and Image Search
Google treats the text in an image alt attribute as part of the page for web search, as well as information about the image itself, for image search.