Image SEO best practices: the 2026 how-to guide (with checklist)

Image SEO is one of the easiest on-page wins going, because most businesses still get the basics wrong.

Most websites treat images as decoration. On your site, every image is three things at once: a ranking asset in Google Images and the regular search results, a Core Web Vitals lever that decides how fast your page loads, and, increasingly, a signal that AI search and Google Lens read to understand your page.

Image SEO is one of the easiest on-page wins going, because most businesses still get the basics wrong. This guide is the full 2026 playbook: a 15-point image SEO best practices checklist, a plain-English image formats comparison (including AVIF), how images drive Core Web Vitals, and what the shift to visual and AI search means for your images. Let’s optimise.

What is image SEO, and how do search engines use images?

Image SEO is the practice of optimising your website images so they help, rather than hurt, your search performance. That means choosing the right image formats, image compression to make pages load fast, writing descriptive alt text and file names, and adding structured data so search engines understand what each image shows. Done well, your website images rank in Google image search results, support the page’s relevance in normal search results, and load quickly enough to keep visitors on the page. (You’ll also see this work called image optimization: same discipline, and a common search term.)

Image SEO matters more in 2026 than it used to, for three reasons. First, image search and Google Images remain a major discovery surface. Second, images are usually the heaviest thing on a page, so they directly control your Core Web Vitals and page speed. Third, AI search and visual tools like Google Lens now read your images, so optimising images is part of being found by AI, not just by classic search engines.

Why images matter for SEO (and revenue)

There’s a direct line from image optimisation to revenue. Heavy, unoptimised images slow your page; a slow page pushes your Largest Contentful Paint past Google’s threshold; a slow-loading page loses visitors before they convert. Tighten your images and you lift both rankings and conversion rate at once.

That’s why we treat image optimisation as a revenue lever in our audits, not a tidy-up task. It’s one of the few jobs that improves rankings, user experience and conversions in a single pass.

The image optimization checklist (image SEO best practices)

Here’s the practical core: 15 steps for optimizing images, in the order we work through them on a site.

1. Have at least one relevant image

Every important page should carry at least one relevant, high-quality image. It can rank in Google Images in its own right, it supports the reader’s comprehension, and it gives multimodal search something to read. A page with no images is a missed image search opportunity.

2. Use high-quality, unique and relevant images

Original images beat generic stock for both users and search engines. Multimodal AI assesses image quality and how well an image matches the surrounding text, so a relevant, original photo or diagram earns more than a recycled stock shot. Where you can, use your own product shots, charts and screenshots.

3. Choose the right image file type

This is where the biggest, fastest wins live. In 2026, Google Search officially supports BMP, GIF, JPEG, PNG, WebP, SVG and AVIF (Google Search Central). The modern best image formats for photos are AVIF and WebP, both of which compress far smaller than JPEG at the same quality. AVIF usually produces the smallest files (often 20–50% smaller than WebP); WebP has the widest support.

You don’t have to choose. Serve a next-gen format with a fallback using the <picture> element. Google specifically recommends it for using new image formats with graceful degradation:

<picture>
  <source srcset="hero.avif" type="image/avif">
  <source srcset="hero.webp" type="image/webp">
  <img src="hero.jpg" alt="Dalmatian puppy playing fetch on a beach" width="1200" height="800">
</picture>

Use SVG for logos and icons (it scales infinitely at a tiny size), and reserve PNG for screenshots or graphics that genuinely need transparency or lossless quality. Always make sure the file extension matches the actual file type.

Best image formats compared

The table compares the main image formats so you can match format to use case at a glance.

Format	Best use	Compression	Transparency	Animation	Browser support 2026	Indexability note
AVIF	Photos, hero images	Lossy/lossless: best	Yes (+ HDR)	Yes	~93%	May index worse than JPEG/PNG in image search*
WebP	Photos + graphics (safe default)	Lossy/lossless: very good	Yes	Yes	~96%	May index worse than JPEG/PNG in image search*
JPEG	Universal photo fallback	Lossy	No	No	Universal	Strong image-search indexing
PNG	Screenshots, transparency, lossless	Lossless (large)	Yes	No	Universal	Strong image-search indexing
SVG	Logos, icons, line art	Vector (tiny)	Yes	Yes	Universal	Not for photos
GIF	Simple animation only	Poor	Yes	Yes	Universal	Use sparingly

*Momentic’s testing suggests WebP and AVIF can be indexed less reliably in Google Images than JPEG and PNG. The practical call: use JPEG or PNG for hero and “money” images you specifically want surfaced in image search, and AVIF/WebP for everything else where speed matters more. Treat this as a working guideline, not a hard rule.

4. Define your image dimensions

Resize images to the dimensions they actually display at. Don’t ship a 4000px file into a 600px slot, because oversized files cost speed for no gain in image quality. Always set explicit width and height attributes on the image tag (or a CSS aspect-ratio) so the browser reserves space and your layout doesn’t jump, which protects your Cumulative Layout Shift score:

<img src="product.webp" alt="Stainless steel drink bottle, 750ml" width="800" height="800">

5. Compress your images

Image compression is the highest-leverage speed fix. Understand the two types: lossless compression removes data without affecting visible image quality (smaller wins), while lossy compression discards some data for much smaller files. The choice between lossy and lossless compression comes down to how much image quality you can spare. For most web photos, lossy at 75–85% quality is invisible to the eye and dramatically lighter.

Good image compression routinely cuts file weight by half or more. As a rule of thumb, keep image files well under a few hundred KB; many sources suggest aiming under ~100KB where the image allows. On WordPress, a compression plugin (ShortPixel, Imagify or Smush) automates this on upload.

To find the images slowing a page, run it through Google PageSpeed Insights. It flags oversized and uncompressed images directly, which is where the Core Web Vitals section below picks up.

6. Customise your image file names

Search engines read file names, so IMG_4521.jpg tells them nothing. Use descriptive, hyphen-separated image file names that describe the image: dalmatian-puppy-fetch.jpg. Set the name before upload. Renaming after the fact is fiddly.

7. Add and optimise the image alt text

Alt text is the most important image SEO signal you control. The alt attribute describes an image to search engines, to screen readers for visually impaired users, and now to multimodal AI, so a good image description does triple duty.

Google’s own good-better-best guidance is the clearest standard for the alt attribute:

• Bad (missing): <img src="puppy.jpg">
• Bad (stuffed): alt="puppy dog pup puppies cheap puppies best puppy" (keyword stuffing breaches Google’s spam policies)
• Better: alt="puppy"
• Best: alt="Dalmatian puppy playing fetch"

Write a clear, contextual image description in the alt attribute that genuinely describes the image, work your keyword in only where it fits naturally, and keep it under roughly 100–125 characters. Good alt text serves accessibility and search engine visibility at the same time, and it’s exactly what AI systems read to understand your visuals.

<img src="dalmatian-puppy-fetch.jpg" alt="Dalmatian puppy playing fetch on a beach" width="1200" height="800">

8. Add image structured data

Structured data helps search engines confirm what an image shows and can earn a prominent badge in Google Images plus eligibility for rich results. Add ImageObject schema markup, and steer which image Google chooses for your page using primaryImageOfPage, an image property on the page’s main entity, or og:image. For ecommerce and photography sites, licensable-image metadata can earn a “Licensable” badge in Google Images.

{
  "@context": "https://schema.org",
  "@type": "ImageObject",
  "contentUrl": "https://example.com/dalmatian-puppy-fetch.jpg",
  "license": "https://example.com/licence",
  "creator": {"@type": "Organization", "name": "Firewire"}
}

9. Use properly licensed (and free) stock photos

When you do use stock, make sure it’s properly licensed. Free libraries like Unsplash and Pexels work for many uses. But remember point 2: unique, relevant images outperform generic stock for both rankings and AI relevance, so original beats free where it counts.

10. Think about the image URL structure

Host images on clean, descriptive, stable URLs. Don’t move or rename them once they’re indexed, and if you serve images from a CDN sub-domain (point 15), keep those paths consistent and verified in Search Console.

11. Make your page title, description and social tags relevant

The page’s own title and meta description give images context, and open graph meta tags control the preview image when your page is shared. og:image can also influence which image Google associates with the page. Set open graph meta tags on every key page so you control the social and preview image rather than leaving it to chance.

12. Make your images mobile-friendly with responsive images

Most visits are mobile, so serve responsive images that adapt to the device. The srcset and sizes attributes let the browser download a right-sized file instead of a desktop-scale image on a phone:

<img src="hero-800.webp"
  srcset="hero-400.webp 400w, hero-800.webp 800w, hero-1600.webp 1600w"
  sizes="(max-width: 600px) 400px, 800px"
  alt="Team reviewing analytics on a laptop" width="800" height="500">

Responsive images cut mobile data and improve mobile LCP, a direct Core Web Vitals win.

13. Add your images to an image sitemap

An image sitemap helps search engines discover visual assets they might otherwise miss. It’s still supported and worth doing in 2026, especially for JavaScript-heavy sites, large galleries, or images served from a CDN (an image sitemap can list image URLs on another domain; just verify that domain in Search Console):

<url>
  <loc>https://example.com/puppies/</loc>
  <image:image><image:loc>https://cdn.example.com/dalmatian-puppy-fetch.jpg</image:loc></image:image>
</url>

14. Lazy-load below-the-fold images

Add loading="lazy" to images below the fold so the browser defers loading them until needed, for a faster initial load and less wasted data. The one rule that matters: never lazy-load your hero or LCP image, because deferring it delays the very thing Core Web Vitals measures.

<img src="footer-diagram.webp" alt="Image SEO workflow diagram" width="900" height="500" loading="lazy">

15. Serve images through a CDN

A content delivery network serves images from a server near the visitor, cutting latency and improving LCP, which is useful for Australian businesses whose hosting or audience sits far from the origin server. Pair it with point 13: verify the CDN image domain in Search Console so those images stay discoverable.

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Image SEO and Core Web Vitals

Here’s the connection most image SEO guides skip: optimising images IS Core Web Vitals work. Your Largest Contentful Paint element, the biggest thing visible when the page loads, is almost always an image, usually the hero. So your image decisions directly set your LCP score.

Optimizing images to improve LCP

Google’s threshold: LCP is “good” at 2.5 seconds or under, “needs improvement” from 2.5 to 4.0 seconds, and “poor” above 4.0 seconds. The image techniques that move it pull straight from the checklist above:

• Compress and correctly size the hero image. It’s the single biggest LCP lever.
• Serve responsive images with srcset/sizes so phones don’t download desktop-scale files.
• Prioritise the hero image with fetchpriority="high" so the browser fetches your LCP element first.
• Lazy-load below-the-fold images only, never the LCP image.
• Set width and height on every image to prevent layout shift and protect your Cumulative Layout Shift score.

Measure it all with Google PageSpeed Insights, which reports your LCP and flags the images holding it back.

The revenue logic is simple: faster image loading lifts LCP, a faster page reduces bounce, and lower bounce means more of your hard-won traffic actually converts. Image optimisation is one of the cleanest speed-to-revenue moves you can make.

Image SEO in the AI era: visual search, Google Lens and AI Overviews

Image SEO used to mean “name the file and add alt text.” In 2026 it’s also about being legible to AI. Multimodal AI systems read images the way they read text, using the surrounding context, on-image text (via OCR), and visual quality to understand what an image shows and whether to surface it. AI Overviews pull images into their answers, and visual tools like Google Lens let people search with their camera rather than a query.

Optimising for Google Images and visual search

The good news: the work that makes images legible to AI is the same work that wins classic image search and traditional Google Images results. Strong Google image SEO and strong AI visibility are the same project.

The trifecta is descriptive alt text, relevant surrounding copy, and ImageObject schema markup. Together they tell both Google’s index and multimodal AI exactly what your image is and why it matters on the page. Clean file names and high-quality, original images reinforce it. Google now publishes an official guide to optimising for its generative AI features, and the underlying advice maps neatly onto this checklist.

Industry estimates suggest visual and AI-assisted search are a fast-growing share of how people find things, though exact figures vary by source. The strategic point holds regardless: as more discovery happens through images and AI answers, the sites whose images are well-described and well-structured get surfaced, and the rest stay invisible.

Frequently asked questions

What image format is best for SEO in 2026 (JPEG vs WebP vs AVIF)?

For photos, AVIF gives the smallest files and WebP the best balance of size and support. Serve them through a <picture> element with a JPEG fallback. Use SVG for logos and icons, and PNG only for lossless or transparency needs. One caveat: testing (Momentic) suggests WebP/AVIF can index less reliably in Google Images, so use JPEG or PNG for hero images you specifically want ranking in image search.

What size should images be for a website?

Size each image to the dimensions it displays at. Don’t load a 4000px file into an 800px space. Compress photos to well under a few hundred KB (aim under ~100KB where quality allows), and always set explicit width and height attributes so the layout doesn’t shift.

Do images affect Core Web Vitals and page speed?

Yes, significantly. Your largest image is usually your Largest Contentful Paint element, and Google wants LCP under 2.5 seconds. Heavy, uncompressed images are the most common reason a page fails Core Web Vitals, so image optimisation is one of the fastest ways to improve both speed and rankings.

Does alt text help SEO or is it just for accessibility?

Both. The alt attribute is read aloud by screen readers for visually impaired users, it tells search engines what an image shows so it can rank in image search, and it helps multimodal AI understand your visuals. Write descriptive, contextual alt text rather than stuffing keywords.

Are image sitemaps still worth it in 2026?

Yes, particularly for JavaScript-heavy sites, large image galleries, or images served from a CDN. An image sitemap helps search engines discover visual assets they might otherwise miss, and it can include image URLs hosted on a separate CDN domain.

How do I get my images into Google Lens and AI Overviews?

Make your images legible to AI: clear alt text, relevant surrounding copy, clean file names, and ImageObject schema, on high-quality original images. That combination tells multimodal systems what the image shows and why it’s relevant, the prerequisite for being pulled into visual search and AI answers.

Do AI-generated images rank?

They can. The same image optimisation rules apply (format, compression, alt text, structured data). But originality and genuine relevance to the page still matter, and a unique, on-topic image generally serves both users and search engines better than a generic generated one.

Small image fixes, big SEO impact

Image SEO is the rare job that improves three things at once: your visibility in image and AI search, your Core Web Vitals, and your conversion rate. None of the 15 steps above is hard. The advantage comes from actually doing them when most of your competitors don’t.

Pick the right image formats, compress and size everything, write alt text that describes the image, and add the structured data that makes your visuals legible to search engines and AI alike. Run the 15-point checklist above across your site, or if you’d rather we turned your images (and the rest of your search presence) into a profitable channel, talk to our team.

Sources and references

1. Google Search Central, Image SEO best practices / Google Images (supported formats incl. AVIF, <picture>/srcset, alt text, structured data, image sitemaps; updated 2 March 2026)
2. Google Search Central, Core Web Vitals / Largest Contentful Paint thresholds
3. Google Search Central, Optimising your website for generative AI features on Google Search
4. Momentic, image format indexability testing (WebP/AVIF vs JPEG/PNG in Google Images)
5. Google PageSpeed Insights, measuring image impact on LCP