Image SEO in 2026: Alt Text, Filenames and Formats That Work
Ammar
AI Specialist

Here is a fact that surprises a lot of store owners: Google does not index CSS background images. If your product photos are set as backgrounds on a div, they are invisible to Google Images no matter how good they look. And if the ones that do get indexed are named IMG00023.JPG with no alt text, Google has very little to go on. Google's image guidance is short and specific, and most of it can be fixed in an afternoon. This post turns it into a checklist: how to mark up images so Google can find them, what to write in alt text and filenames, which formats are supported, and how to check your own pages.
Rule one: use real img elements
Google finds images in the src attribute of an element, including when the tag sits inside a
is the recommended form.
This is the first thing to check on carousels, hero sections and product galleries built with scripts or page builders.
Rule two: write alt text like you mean it
Google calls alt text the most important metadata for an image. It helps accessibility, helps Google understand the image, and acts as anchor text if the image is a link. Google's own examples show the ladder:
| Quality | Example | Why |
|---|---|---|
| Bad | (no alt attribute) | Google and screen readers get nothing |
| Bad | puppy dog baby dog pup puppies | Keyword stuffing, which can be seen as spam |
| Better | puppy | Accurate but thin |
| Best | Dalmatian puppy playing fetch | Specific, descriptive and in context |
For a store, the same logic gives you "Black mesh running shoes for men, side view" instead of "shoes". For an inline SVG, Google says to use a
Rule three: name files for humans
Google recommends short, descriptive filenames. my-new-black-kitten.jpg is better than IMG00023.JPG, and generic names like image1.jpg are best avoided. If you localise a page, translate the filenames too. If your product photos come off a camera or a supplier's drive, rename them in bulk before you upload.
Rule four: put images next to the words that explain them
Google uses the content around an image, including captions and image titles, to understand it. Place an image near text on a page that matches its subject. A product photo on a product page with a clear heading and description does this by default. A photo dropped onto an unrelated page does not.
Formats, size and speed
Google supports BMP, GIF, JPEG, PNG, WebP, SVG and AVIF, and says the file extension should match the real file type. It does not name a winner among them. Images are often the largest share of a page's weight, so compress them and check the page in PageSpeed Insights. Sharp images also look better as thumbnails. Data URIs are allowed, but Google warns they can noticeably increase page size, so use them sparingly. Slow images also hurt your Core Web Vitals, which we cover in our guide to passing LCP, INP and CLS.
Responsive images: always keep a fallback
You can serve different sizes with srcset and sizes on the img element, or with the

Image sitemaps and CDNs
An image sitemap can surface images Google might not otherwise find. It can list image URLs hosted on other domains, so a CDN works. If you use a CDN, Google says to verify its domain in Search Console so you can see any crawl errors.
Structured data for images
Adding structured data can make images eligible for a badge and rich results in Google Images. The image property is required for eligibility, and you need to follow both the general and the type-specific guidelines. If you already add Product markup, check that its image property points at a real, crawlable image.
A 20-minute image audit
• Open your top three product or landing pages and view the source. Is each key image an element, not a CSS background?
• Check the alt text on those images. Is it missing, stuffed, or thin?
• Look at the filenames. Rename any that look like IMG_4821.jpg or image1.jpg.
• Confirm every responsive image has a plain src fallback.
• Run a key page through PageSpeed Insights and note the heaviest images.
• If your images live on a CDN, confirm its domain is verified in Search Console.
If you sell online, our guides on Shopify development for Delhi NCR brands and AI-ready product feeds are good next reads.
FAQ
Does Google index CSS background images?
No. Google finds images in the src attribute of img elements, including inside picture elements. A background set in CSS is not indexed.
How long should alt text be?
Google gives no length. Its guidance is to be specific, descriptive and in context, and to avoid keyword stuffing. "Dalmatian puppy playing fetch" is its example of best.
Which image format should I use?
Google supports BMP, GIF, JPEG, PNG, WebP, SVG and AVIF, and does not pick a favourite. Compress whatever you use and keep the file extension consistent with the real file type.
Do filenames matter?
Google recommends short, descriptive filenames and gives my-new-black-kitten.jpg as better than IMG00023.JPG. Avoid generic names such as image1.jpg.
Do I need an image sitemap?
It is not required, but Google says image sitemaps can surface images it might not otherwise find, and they can list images hosted on a CDN.
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Key Takeaways
- • Google indexes images in
elements, not CSS backgrounds.
- • Alt text is the most important image metadata: be specific and descriptive, never stuffed.
- • Use short, descriptive filenames instead of camera names like IMG00023.JPG.
- • Always keep an
fallback when you use srcset or
. - • Add an image sitemap if Google may miss images, and verify your CDN domain in Search Console.
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