Image SEO: Getting Your Images Found

On almost every Australian site I audit, the images are doing heavy lifting for the brand and nothing for search. They are exported as IMG00023.JPG, dropped in with no description, and never looked at again.

I have spent 13 years working on search, and image work is one of the few areas where an afternoon of effort usually shows a measurable result. It is also one of the most over-written topics online, which is why so many owners end up doing the low-value half of it and skipping the part that matters.

This is for the owner or marketing manager who suspects their images are invisible in image search and possibly making pages heavier, but cannot tell which of the many tips doing the rounds are worth the time. It covers how images are discovered, the two changes with the highest return, how to pick a file format without turning it into a project, how to send the right number of pixels, where lazy loading helps and where it hurts, and how image discovery reaches past your own pages.

Why image SEO is worth an hour of your time

Images sit on nearly every page

Images are not a niche part of a website. They are on nearly all of it. Per the Web Almanac, "It comes at no surprise that of the more than 10 million scanned and parsed pages, 99.9% requested at least one image."

That single figure tells you why image work scales. Whatever you fix on one page tends to apply across the rest of the site, because the same habits and the same missing details repeat everywhere.

The two places images earn attention

Images earn attention in two places. The first is image search itself, where a well-named, well-described image can bring people to a page you would not otherwise reach with that photo. The second is the page a person lands on, where the image either supports the message or gets in the way of it loading.

Everything below is aimed at those two outcomes. If a change does not help an image get found or help the page behave, it is a detail worth skipping.

How Google finds your images

Standard image elements and what Google skips

Most images are found the ordinary way: Google reads the page, follows the image references in the markup, and fetches the files. That path covers the standard image element and the newer ways of loading an image on a modern site.

Some images it never picks up. Per Google Search Central, "Google doesn't index CSS images." A background image set in a stylesheet is not treated as an image on the page, so it will not appear in image search no matter how good its alt text is. If an image carries meaning, it belongs in the page markup, not just in the stylesheet.

Image sitemaps and images hosted on a CDN

Images that a crawler cannot reach by following the page need another route in. Per Google Search Central, "You can provide the URL of images we might not have otherwise discovered by submitting an image sitemap."

That matters when the site is large, when images sit behind a script, or when the files are served from somewhere other than the main domain. A content delivery network is a common example, and it is covered later in this piece.

Filenames and alt text that do real work

Writing filenames a person could read

A filename is a light signal, but it is free to fix and easy to read. A file called red-leather-office-chair.jpg says what the picture is. A file called IMG_4471.jpg says only that a camera produced it.

Do not turn it into a sentence or stuff it with phrases. Lower case, words separated by hyphens, and a plain description of what the image shows. That is the whole standard.

Alt text that describes, rather than repeats keywords

Alt text is the one that most sites are missing. Per the Web Almanac, "Unfortunately, 45 percent of <img> elements don't have any alt text."

Alt text describes the image for someone who cannot see it, and search engines read it as context for the picture. Write what the image shows, in a sentence a person would understand. Repeating a keyword in every alt attribute adds nothing and reads as noise.

Captions, surrounding text and image titles

Captions and the text around an image do more than most people expect, because they explain the image in the context of the page. A photo of a finished kitchen means more when the paragraph beside it names the suburb and the problem it solved.

Image titles are weaker and often unused. Fix the filename, the alt text and the caption first, and treat the title as a minor extra.

Choosing a format without overthinking it

JPEG, PNG, WebP and AVIF in plain terms

For photographs, use JPEG or WebP. For graphics with flat colour, sharp edges or transparency, use PNG or a vector format. Newer formats such as WebP and AVIF give you a smaller file at similar visual quality, and current browsers support them well.

You do not need a rule for every case. Match the format to the kind of image and move on. A photo saved as a huge PNG is the mistake worth catching, and not much else.

What the data says about what the web actually serves

It is worth knowing what the wider web does, because it shows how much room there is. Per the Web Almanac, "JPEG comes in first, at 32.4%."

An older format still leading says most sites have not moved on yet. That is an opportunity rather than a problem. Switching a few heavy images on your busiest pages to a modern format is a contained job with a visible result.

Sizing and responsive images

Sending the right number of pixels

The most common cause of a slow image is size. A photograph exported at full camera resolution, then displayed in a small box on the page, sends far more pixels than the screen will ever show.

Export each image at the size it is actually displayed, with a little room for larger screens. If an image sits in a space 600 pixels wide, a 4000 pixel file is wasted weight on every visit.

When srcset and sizes are worth the effort

Responsive images let you offer several versions of the same picture and let the browser choose. On a site with a lot of photography, that is a real improvement for the visitor.

On a small site with a handful of images, it is often not worth the build time. Pick the ones that matter, the hero images and the large photos, and leave the rest at a sensible single size.

Lazy loading: use it, but not everywhere

The image you should never lazy load

Lazy loading means an image is only fetched when it is about to be needed, which saves work on a long page. Applied to the wrong image, it does the opposite.

Per the Web Almanac, "Lazy-loading the LCP element is an anti-pattern that makes pages much slower." In plain terms, the main image at the top of the page is the one a visitor is waiting for, and delaying it is a mistake. Lazy load below the fold only.

Checking what your pages load first

The idea has spread quickly. Per the Web Almanac, "Lazy-loading was introduced in 2020, and just two years later it was adopted on almost a quarter of websites."

Open your own page and watch what loads first. If the top image is waiting on a scroll that has not happened, that is the one to change. Everything further down can keep the lazy setting.

Image discovery beyond your own pages

Image sitemaps and CDN hosted files

Images served from a content delivery network are still your images, and they can still be found. Because the file sits on another domain, an image sitemap is the straightforward way to point at it.

It also helps to verify the other domain in Search Console, so any problem with the image files reaches you rather than going unnoticed.

Structured data and image rich results

Some image surfaces draw on structured data, which is a separate job from the naming and description work described above. Where it applies, it is worth doing, but it does not replace the basics.

Get the filename, alt text, caption and file size right first. Those changes help on every image surface, structured data or not.

A quarterly image routine

The checks to run and who runs them

Once a quarter, open the pages that matter most and check four things: the filename, the alt text, the file size and whether the top image is lazy loaded by mistake. Fix what fails, then move to the next page.

If somebody publishes content, they own the naming and the alt text for their own images. The size and loading checks are better handled by whoever manages the site.

What to measure afterwards

Give the change a few weeks, then look at your image search data and your page loading, rather than your rankings overall. Image work shows up in image results and page behaviour before it shows up in anything broader.

If you want the full picture rather than one page at a time, the technical SEO checklist, images included covers the ground in order, and getting the visuals right in your content is the wider piece this sits inside. There is work on a visually led site in the case studies if you want to see how image-heavy content is handled, and the same files are often worth reusing the same image assets on social rather than exporting them twice.

Frequently asked questions

How much does alt text actually matter for SEO?

It matters, and the data says most sites are not doing it: the Web Almanac's 2024 crawl found 45 percent of image elements with no alt text at all. Alt text is primarily a description of the image for people who cannot see it, and Google reads it as context. Write what the image shows, in a sentence a person would understand.

Should I rename every image on my site?

No. Start with the images on your highest traffic pages and your commercial pages. Descriptive filenames are a light signal, and the work is only worth doing where the image already sits on a page that matters.

Which image format should I use?

For photographs, JPEG or WebP. For graphics with flat colour, PNG or SVG. Newer formats such as WebP and AVIF give you smaller files at similar quality. The Web Almanac's 2024 crawl showed JPEG still the most common format served, at 32.4%, which tells you how much room most sites have to improve.

Does lazy loading help or hurt?

It helps for images far down the page and hurts for the main image at the top. The Web Almanac describes lazy loading the largest contentful image as an anti-pattern that makes pages slower. Lazy load below the fold only.

Can Google find my images if they are hosted on a CDN?

Yes. Google's image sitemap documentation allows URLs from other domains, which is exactly how CDN hosted images get discovered. Verify ownership of the CDN domain in Search Console so you hear about crawl problems.

Will fixing images improve my rankings?

I would not promise that. Fixing images reliably improves how often your images surface in image search and how the page loads, and it removes a genuine barrier to being understood. Treat it as good hygiene with a visible upside, not as a ranking lever you can pull on its own.