Overview
Image SEO is the process of making website images easier for search engines to discover, understand and display in search results, while keeping them fast and accessible for users. This includes choosing suitable file formats, compressing images, using descriptive filenames and alt text, supplying appropriate dimensions and making sure important images can be crawled and indexed.
Images can be easy to overlook when optimising a website. Most SEO work naturally focuses on written content, page structure, links and technical issues, but the images used throughout a site can also affect search visibility, accessibility and page performance.
Google can surface images in several places, including standard search results, Google Images and visual search experiences such as Google Lens. This means an image may sometimes become somebody’s first interaction with your website rather than simply supporting the page it sits on.
Why should you use images within your content?
Images can make detailed information easier to understand. A product photograph can show something that would take several paragraphs to describe. A diagram can explain how a process works, while a photograph of a finished project can give a potential customer useful context before they make an enquiry.
Images also break up longer sections of text and can make pages easier to scan.
However, every image adds another file that the visitor’s browser needs to load. Images should therefore have a clear purpose rather than being added simply to fill space.
A useful question to ask is: would somebody understand this page less clearly if this image disappeared? If the answer is yes, the image is probably contributing something worthwhile.
Which image file format should you use?
The most suitable file format depends on what the image contains and how it will be used.
JPEG remains widely used for photographs because it can produce reasonably small files while preserving enough detail for web use.
PNG is often useful where transparency or very crisp graphic elements are needed, although PNG files can become considerably larger than equivalent photographic formats.
GIF is still used for simple animation, but it is rarely the most efficient choice for detailed imagery.
More modern formats such as WebP and AVIF can provide good image quality at smaller file sizes. Browser support for both is now broad enough that they can be practical choices on modern websites.
You do not need to convert every existing image simply because a newer format exists. The aim is to deliver an image that looks good enough for its purpose without requiring visitors to download unnecessary data.
How should you name images for SEO?
An SEO-friendly image begins with a clear filename. Camera uploads and stock images often arrive with filenames such as:
IMG_4827.jpg
or:
DSC00126.png
Those names tell search engines very little about what the image contains. A descriptive filename is more useful.
For example:
birmingham-office-interior.jpg
provides more context than:
image123.jpg
Google states that filenames can provide light clues about the subject of an image, so short and descriptive wording is worthwhile.
Avoid trying to insert every target keyword into the filename.
If the photograph shows a commercial kitchen extraction system, a filename such as:
commercial-kitchen-extraction-system.jpg
is useful.
A filename such as:
commercial-kitchen-extraction-system-best-kitchen-extraction-birmingham-cheap.jpg
adds clutter without making the image easier to understand.
Describe what is actually shown.
What is image alt text and why does it matter?
Alt text, sometimes called an alt attribute or alt tag, provides a written description of an image.
It is particularly important for accessibility because screen readers can use it to explain the content of an image to somebody who cannot see it.
Alt text can also help search engines understand what an image represents. Google says that it uses alt text alongside page content and computer vision when interpreting images.
For example, an image might use:
alt=”Engineer inspecting an electrical control panel”
This is more useful than:
alt=”control panels electrical control panels Birmingham control panel manufacturer”
The first describes what somebody can actually see.
The second has been written around keywords rather than the image.
Alt text should usually provide enough information for somebody to understand why the image is relevant to the page.
Decorative images are different. If an image adds no meaningful information, it may be appropriate to use an empty alt attribute so that a screen reader can move past it without unnecessary interruption.
Should image title attributes be used?
Image title attributes can provide additional information when somebody interacts with an image, but they should not be treated as a substitute for alt text.
Alt text serves a specific accessibility and descriptive purpose.
For most everyday SEO work, making sure that meaningful images have accurate alt text is more important than spending time creating separate title attributes for every image.
If a title attribute is used, keep it useful and avoid duplicating keyword-heavy wording purely for SEO.
How does Google Lens change image SEO?
Google Lens allows people to search using an image rather than relying entirely on typed words.
A user might photograph a product, building, plant, item of clothing or piece of machinery and use Lens to identify it or find visually similar results.
That changes the role of images in search.
A search engine is no longer relying solely on the words surrounding an image. Google’s systems can analyse the visual content itself and combine what they see with other information about the page. Google also directs websites seeking visibility in Lens towards its wider image SEO best practices.
For businesses, this means original, clear images can have more value than they once did.
Google recommends placing high-quality images close to text that is relevant to what the image shows.
What do Google Lens and visual search mean for filenames and alt text?
Visual recognition does not make filenames and alt text redundant. Google can analyse what appears within an image, but descriptive text provides additional context.
Imagine a photograph showing a specialist industrial component.
Computer vision may recognise its basic shape or material, but the filename, alt text and nearby copy can explain its exact purpose, specification or application.
A sensible combination might be:
Filename:
stainless-steel-flange-nut.jpg
Alt text:
Stainless steel flange nut with serrated base
Nearby copy could then explain where that particular type of fastener is normally used. Each element contributes slightly different information. This is more useful than repeating exactly the same keyword everywhere.
How large should website images be?
There are two different types of image size to think about: dimensions and file size.
Dimensions describe the width and height of the image in pixels.
File size describes how much data the visitor needs to download.
A common mistake is uploading a photograph that is 4,000 pixels wide and then displaying it on the website at only 600 pixels wide. The browser may still need to download the much larger original file.
Resize images according to how they will actually be displayed.
Modern websites should also use responsive images where appropriate so browsers can select a suitable image for different screen sizes.
A large desktop monitor may require a larger image than a mobile phone.
Google recommends responsive image techniques because they can improve how images are delivered across different devices.
Why should images be compressed?
Image compression reduces file size while attempting to preserve acceptable visual quality. This matters because large image files can make pages noticeably slower.
Consider a page containing ten photographs at 2MB each. A visitor could potentially need to download around 20MB of image data before accounting for the rest of the page.
Compressing those photographs to a few hundred kilobytes each can dramatically reduce the amount of information being transferred.
The correct level of compression depends on the image. A detailed product photograph may need to retain more clarity than a small supporting image within a blog article.
Inspect the final result rather than choosing a compression percentage automatically. If you can clearly see unwanted artefacts or blurred detail, the file has probably been compressed too aggressively.
Should you use lazy loading for images?
Lazy loading delays the loading of certain images until they are likely to be needed. For example, a photograph near the bottom of a long article does not necessarily need to download the moment somebody opens the page.
Loading it as the visitor approaches that section can reduce the amount of data required during the initial page load. This can be particularly useful on image-heavy pages.
However, important images that appear immediately at the top of a page should generally not be unnecessarily delayed.
Lazy loading also needs to be implemented in a way that allows search engines to discover the images. Google warns that poorly implemented lazy loading can hide content from its crawlers, particularly when loading depends on somebody clicking or manually scrolling.
Browser-based lazy loading is now commonly used for suitable images.
What is an image sitemap?
An image sitemap helps Google discover images on your website. Image information can either be included within an existing XML sitemap or supplied through a dedicated image sitemap.
This can be particularly useful where images are harder for crawlers to discover through normal webpage links or where JavaScript is involved in displaying them.
Google specifically recommends image sitemaps as a way of informing it about images that it might otherwise fail to find.
For a small website where every important image is already clearly embedded in crawlable HTML pages, an image sitemap may offer less practical benefit.
For larger ecommerce, publishing or image-led websites, it is worth reviewing.
If images are hosted on a separate content delivery network, make sure search engines can access those files and that robots.txt rules are not accidentally blocking them.
How should images be embedded on a webpage?
Where possible, important images should be included using standard HTML image elements. Google specifically identifies images referenced within the src attribute of an <img> element as discoverable.
Images used purely as CSS backgrounds are treated differently and Google does not index them in the same way.
That distinction matters if a particular image has search value.
For example, an ecommerce product photograph should normally be implemented as an actual page image rather than being used only as a decorative background.
Can images appear as thumbnails in Google Search?
Yes. Google can display image thumbnails alongside ordinary search results where it considers them relevant.
The website does not choose exactly when a thumbnail appears, but making useful images crawlable and following Google’s image SEO guidance can improve the information available to Google’s systems.
For article and service pages, the main image should therefore be relevant to the subject rather than a generic stock photograph chosen simply because it looks attractive.
If somebody sees a thumbnail beside a search result, it should reinforce what the page is actually about.
Where should images appear within the page?
Images should normally sit close to the content they support. A diagram showing how a heating system works is most useful beside the section explaining that process.
Placing it somewhere unrelated makes the connection less clear for both the reader and search engines.
Captions can also help where an image needs explanation. For example, a photograph of specialist equipment might benefit from a short caption explaining the model, application or stage of a process being shown.
There is no need to add captions to every photograph. Use them when they give the reader information they would not otherwise have.
How can you check whether your images are optimised?
A basic image SEO review can be done page by page.
Check whether:
- important images have descriptive filenames
- meaningful images contain useful alt text
- decorative images are treated appropriately
- photographs are compressed
- image dimensions are sensible for their display size
- suitable modern formats are being used
- important images can be crawled
- lazy loading is working correctly
- images sit beside relevant copy
- high-value images can be found in Google Images
- image sitemaps are appropriate for the website.
You can also use Google Search Console to understand whether image-led searches contribute to visibility.
Google Images supports operators such as src: and imagesize: for investigating indexed images, although Google advises using Search Console tools for more reliable debugging.
What makes an image SEO-friendly?
An SEO-friendly image should be useful to the person viewing the page, accurately described and delivered efficiently.
In practical terms, that usually means starting with a clear image, choosing an appropriate format, resizing and compressing it, using a descriptive filename and writing useful alt text.
From there, make sure important images are embedded in crawlable HTML, positioned beside relevant content and included in an image sitemap where that genuinely helps discovery.
Visual search means search engines can understand more about what appears inside an image than they could in the past, but the supporting information around that image still matters.
The strongest approach is therefore quite straightforward: use images that genuinely help explain the page, describe them accurately and avoid making visitors download more data than they need.