Image SEO is the practice of optimizing your images so they help rather than hurt your site, earning you image search traffic, faster pages, better accessibility, and clearer understanding by search engines and AI. Most sites ignore their images and leave this value on the table. Below: how to name image files, alt text that works and where Google draws the line, formats and compression, the lazy loading mistake that costs you LCP, image sitemaps and structured data, and the WordPress specifics.
How to name image files
Naming your image files well is the first step, and it must happen before you upload, since renaming after upload is a chore in most content systems. A descriptive file name helps search engines understand what the image shows. Use clear, keyword aware names with words separated by hyphens, and describe the actual image.
Right: a file named red-running-shoes.jpg for a photo of red running shoes. Wrong: a file named IMG_4821.jpg or photo1.jpg, which tells search engines nothing. The rule is simple: rename your images to describe their content in plain words before uploading, avoiding camera default names and random strings.
This small habit, done at upload time, gives every image a clear signal and is one of the easiest image SEO wins available.
Alt text that works
Alt text, the alternative text attribute, describes an image for people using screen readers and for search engines when the image cannot load. Write it for accessibility first and search second, describing the image clearly and naturally. Here are examples across contexts.
For a product photo, right: a woman wearing a blue waterproof hiking jacket; wrong: jacket, or a keyword stuffed jacket buy cheap jacket. For an infographic, describe its key point, not just infographic. For a photo with text, include the important text.
For a decorative image that adds no information, the right approach is an empty alt attribute so screen readers skip it, rather than forcing a description. For a chart, summarize what it shows. For a logo, name the brand.
The pattern throughout is to describe the image honestly and helpfully for a person who cannot see it, including your keyword only where it fits naturally. Good alt text serves real users first, and that is exactly what also serves search engines, since honest, descriptive alt text both improves accessibility and helps your images rank.
Worth knowing where the line sits, because Google states it explicitly. Its image guidance calls alt text the most important attribute for describing an image, and asks for useful, information rich text that fits the context of the page. It then warns directly that stuffing keywords into alt text creates a poor user experience and may cause a site to be seen as spam.
The test that keeps you on the right side of that: write the alt text for someone who cannot see the image and needs to know what it shows. If the sentence only makes sense to a search engine, rewrite it.
Image formats and compression
The format and size of your images strongly affect page speed, so optimize them practically. Modern formats like WebP and AVIF offer much smaller file sizes than older formats like JPEG and PNG at similar quality, so using them where supported makes your pages faster. Many tools and plugins can convert and serve these modern formats automatically.
Whatever the format, compress your images before or during upload to reduce file size, since large uncompressed images are a leading cause of slow pages. Here are the working numbers, because “as small as possible” is not an instruction anyone can follow.
Images are typically 40 to 60 percent of a page’s total weight, which is why they are the first place to look when a page is slow rather than the last.
Export at 75 to 85 percent quality. This is the range where lossy compression stops being visible to a viewer and still removes most of the file size. Below about 70 you start seeing artefacts in gradients and skin tones; above 90 you are paying real bytes for a difference nobody can see.
Aim to keep most images under 200KB. Hero images can justify more, thumbnails should be far less, but if a normal in content image is above 200KB it has almost certainly been exported straight from a camera or a design tool without a second thought.
On AVIF versus WebP: AVIF compresses photographs roughly 15 to 20 percent better than WebP, but it encodes much more slowly. The sensible default is WebP for everything, reaching for AVIF only where file size genuinely matters, such as a large hero on a page you care about above all others.
The practical goal is still the quality versus weight tradeoff: find the point where the image still looks good but weighs as little as possible, since a visitor rarely notices slight compression but definitely notices a slow page. Use a good compression tool or an optimization plugin, choose modern formats where you can, and size images appropriately for how they display rather than uploading enormous originals.
Done right, your images look great and load fast, which both users and search engines reward.
Lazy loading, dimensions, and CLS
Three technical touches keep image heavy pages fast and stable. Lazy loading means images below the visible area load only as the user scrolls to them, which speeds up the initial page load, and most modern platforms support it easily. Specifying image dimensions, the width and height, lets the browser reserve the right space before the image loads, which prevents the page from jumping around as images appear.
That jumping is called cumulative layout shift, or CLS, a real user experience problem and a ranking signal, and setting dimensions is the main fix for image related layout shift. Together, lazy loading speeds the load, and set dimensions keep the layout stable, so combining them gives you fast, smooth pages even with many images. Most content systems and optimization plugins handle these automatically or with a simple setting, so you rarely need to code them by hand, but knowing why they matter helps you make sure they are enabled.
The lazy loading mistake that costs you LCP
Lazy loading is good advice with one important exception, and WordPress users hit it by default.
Lazy loading tells the browser not to fetch an image until it is needed. Applied below the fold, it saves real bandwidth. Applied to the image at the top of the page, it does the opposite of what you want: the browser deliberately delays the very image that determines your Largest Contentful Paint.
The numbers come from research published on web.dev, run against WordPress’s own default behaviour. Lazy loading images in the initial viewport produced an LCP regression of 13% on desktop and 15% on mobile for archive pages. The cause was network contention: the browser was busy fetching other things while the image that decides your score waited its turn.
The fix is not to switch lazy loading off. When above the fold images were exempted while everything below stayed lazy, archive pages improved by 14 to 18% against the default, and the bandwidth savings were fully retained.
So the rule is: eager load what is in the first screen, lazy load everything after it. In practice that means your featured image, hero image or first in content image should not carry loading=”lazy”, and everything further down should. Modern WordPress versions try to do this automatically by skipping the first image, but plugins that add their own lazy loading frequently override it and reintroduce the problem, so check your actual HTML rather than assuming.
The quick check: load a post, view source, and look at the first image tag. If it has loading=”lazy” and it is visible without scrolling, that is your LCP being slowed on purpose.
Image sitemaps and structured data
Two extras matter in specific cases. An image sitemap, or including images in your regular sitemap, helps search engines discover your images, which is useful if images are important to your site, like a photography portfolio or a large product catalog, though many sites do not need a separate one. Structured data, such as marking up product images or recipe images with schema, helps search engines understand and potentially feature your images in rich results, which matters most for ecommerce, recipes, and similar content.
For a typical blog or small business site, these are nice to have rather than essential, and good content systems often handle image sitemaps automatically. Focus first on naming, alt text, formats, and speed, then add image sitemaps and structured data if your site type genuinely benefits from surfacing images prominently in search.
Image SEO for WordPress
On WordPress specifically, image SEO is straightforward with a few habits and tools. Rename your image files descriptively before uploading, since WordPress uses the file name, and add alt text in the media library for each image, which WordPress makes easy in the attachment details. Use an image optimization plugin to compress images and serve modern formats like WebP automatically, which handles much of the speed work for you.
Be mindful of the multiple image sizes WordPress generates, and manage them so you are not serving unnecessarily large files or creating clutter, as covered in our guide on WordPress image sizes. Modern WordPress also supports lazy loading by default. With a good optimization plugin, descriptive file names, proper alt text, and sensible image sizes, WordPress makes image SEO manageable without technical skill, so you get faster pages and better image visibility with modest effort.
Verdict checklist
Image SEO is easy value most sites ignore, so run through this checklist. Rename image files descriptively before uploading. Write honest, helpful alt text for accessibility first, using an empty alt for purely decorative images.
Use modern formats like WebP and compress every image to balance quality and weight. Enable lazy loading and set image dimensions to keep pages fast and stable and avoid layout shift. Add image sitemaps and structured data only if your site type benefits.
On WordPress, use an optimization plugin and manage your image sizes. Do these, and your images earn search traffic, speed up your pages, improve accessibility, and help search engines and AI understand your content, which is a lot of value for modest effort. This on page image work is distinct from publishing images elsewhere, covered in our guide to image submission sites.
Frequently asked questions
What should I name my image files?
Name your image files with clear, descriptive words that reflect what the image shows, separated by hyphens, before uploading. For example, name a photo of red running shoes red-running-shoes.jpg rather than IMG_4821.jpg or photo1.jpg. Descriptive file names help search engines understand your images and can help them rank in image search. Do this at upload time, since renaming afterward is a chore in most content systems, and avoid camera default names and random strings.
Does alt text help SEO?
Yes, alt text helps SEO by describing your images to search engines, which can help them rank in image search and improves how search engines understand your page. Just as importantly, alt text is essential for accessibility, describing images for people using screen readers. Write it honestly and descriptively for people first, including your keyword only where it fits naturally. Good alt text serves real users and search engines together, so it is well worth adding to every meaningful image.
What image format is best for websites?
Modern formats like WebP and AVIF are generally best for websites, since they offer much smaller file sizes than older JPEG and PNG at similar quality, making pages faster. WebP is widely supported and a great default. Whatever format you use, compress your images to reduce weight. Many tools and plugins can convert images to modern formats automatically, so you get faster pages without extra effort, which both users and search engines reward.
Do images slow down my site?
Large, uncompressed images are one of the most common causes of slow websites, so unoptimized images definitely slow your site. However, optimized images do not have to. By using modern formats like WebP, compressing every image, sizing them appropriately, and enabling lazy loading, you can have plenty of images with minimal speed impact. The problem is not images themselves but unoptimized ones, so a little image optimization keeps your pages fast and image rich at the same time.
Should I lazy load all my images?
No. Lazy load everything below the fold and eager load what appears in the first screen. Research published on web.dev found that lazy loading images in the initial viewport regressed LCP by 13 percent on desktop and 15 percent on mobile, while exempting above the fold images improved archive pages by 14 to 18 percent and kept all the bandwidth savings.
Can you over optimise alt text?
Yes, and Google says so directly. Its image guidance calls alt text the most important attribute for describing an image, then warns that stuffing keywords into it results in a negative user experience and may cause a site to be seen as spam. Write it for someone who cannot see the image; if the sentence only makes sense to a search engine, rewrite it.
How small should my images be?
Keep most in content images under 200KB, and export at 75 to 85 percent quality, which is where lossy compression stops being visible while still removing most of the file size. Images usually make up 40 to 60 percent of a page’s total weight, so this is the first place to look when a page is slow. Hero images can justify more; thumbnails should be far less.
Should I use AVIF or WebP?
WebP as the default, AVIF only where size genuinely matters. AVIF compresses photographs about 15 to 20 percent better than WebP, but it encodes considerably more slowly, which becomes a real cost when you are processing many images. For a large hero on an important page the extra saving is worth it; for everything else the difference does not justify the slower workflow.